JPH08326608A - Exhaust reflux control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve responsiveness of exhaust reflux control and prevent occurrence of malfunction of a motor by setting a driving frequency of a step motor high when pressure difference across an exhaust circulation valve is small. CONSTITUTION: Pressure difference across an exhaust reflux valve 5 is sensed by means of a pressure difference sensor 18. A coil temperature sensor 19 senses a temperature of a coil of a step motor 6. In an exhaust reflux valve 5 with the step motor 6 being an actuator, a reference frequency is set higher in a table as the pressure difference across the exhaust circulation valve 5 is small. As the coil temperature sensed by the coil temperature sensor 19 is high, maintenance current to be supplied to the step motor at the stoppage of the exhaust reflux valve 5 based on the coil temperature is set higher. The reference frequency is corrected to be a smaller value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device for an internal combustion engine, and more specifically, it is equipped with an exhaust gas recirculation valve in an exhaust gas circulation path for recirculating a part of exhaust gas to an intake pipe. The present invention relates to an exhaust gas recirculation control device configured to adjust an exhaust gas recirculation amount by driving.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas recirculation control device for an internal combustion engine, there is one having a structure as shown in FIG.
-301170 gazette etc.). In FIG. 21, an internal combustion engine 1 is provided with an exhaust circulation path 4 that connects an intake manifold (intake pipe) 2 and an exhaust manifold 3 to each other.
Part of the exhaust gas is recirculated to the intake manifold 2 via the exhaust circulation path 4 due to the pressure difference between the intake and exhaust systems.

An exhaust gas recirculation valve 5 for adjusting the exhaust gas recirculation amount by changing the effective opening area of the exhaust gas circulation path 4 is provided in the exhaust gas circulation path 4. The exhaust gas recirculation valve 5 is a valve that adjusts the amount of exhaust gas recirculation according to its lift amount. The exhaust gas recirculation valve 5 converts the rotational movement of the step motor 6 into a linear movement as an actuator, and is biased in the valve closing direction by the coil spring 7. Open the valve by lifting the existing valve body from the valve seat.

The engine control computer 8 includes the engine 1
The air flow sensor 9 for measuring the intake air flow rate, the crank angle sensor 10 for detecting the crank angle, the water temperature sensor 11 for detecting the cooling water temperature, the idle switch 13 for detecting the fully closed position of the throttle valve 12, the engine intake air-fuel mixture Oxygen sensor 14 that detects the oxygen concentration in the exhaust gas that is closely related to the air-fuel ratio
The detection signals from the same are input.

Then, the engine control computer 8 is
The fuel injection amount and the ignition timing are calculated based on the detection signals from the various sensors, and the fuel injection valve is calculated based on the calculation result.
The fuel injection amount and injection timing by 15 and the ignition timing of the spark plug 16 are controlled. Further, the engine control computer 8
Calculates an exhaust gas recirculation amount (a target opening degree of the exhaust gas recirculation valve 5) based on detection signals from the air flow sensor 9, the crank angle sensor 10, etc., and outputs a pulse signal to the step motor 6 based on the exhaust gas recirculation amount. Is output to drive the exhaust gas recirculation valve 5 to a predetermined opening degree.

Here, when the target opening degree of the exhaust gas recirculation valve 5 does not change due to steady operation or the like, the coil spring 7
In order to keep the opening degree constant against the valve closing biasing force, the energization is continued for the last excited motor excitation phase.
At this time, the power consumption is reduced by chopping the energizing current of the step motor, thereby improving the fuel consumption and suppressing the self-heating of the coil in the step motor.

In FIG. 21, 17 is a three-way catalyst for purifying exhaust gas.

[0008]

In the conventional exhaust gas recirculation control device described above, the drive frequency of the step motor and the holding current (chopping control) for keeping the opening constant regardless of the operating state. And a fixed drive frequency and a holding current are set as follows.

If the coil temperature of the step motor rises due to heat transfer from the exhaust gas or self-heating, the increase in coil resistance will reduce the energizing current and reduce the motor torque, which will likely cause step-out of the motor. . Therefore, even when the exhaust gas recirculation valve is fully opened, the valve closing bias of the coil spring is maximum, the amount of heat transferred from the exhaust is maximum, and the motor torque is minimum. In addition, it is necessary to set the fixed drive frequency to a relatively low value, set the fixed holding current to a relatively large value, and set the motor torque to a large value with a margin.

Further, when the exhaust gas recirculation valve is controlled to have a low opening degree and the engine load is low and the differential pressure between the upstream and downstream of the exhaust gas recirculation valve is high, intake pulsation and rotation fluctuations occur and the exhaust gas recirculation valve is caused. However, if the drive frequency is high at this time, the motor may be easily out-of-step due to frequent reverse rotation. Therefore, it is necessary to keep the drive frequency relatively low. .

As described above, in the prior art, in order to prevent the occurrence of step-out, the drive frequency was suppressed to a relatively low value, and the holding current was set to a large value with a margin, so that there were the following problems. That is, since the holding current is set to a relatively high value that satisfies the requirement when the exhaust gas recirculation valve is fully opened, the holding current becomes excessively large except when the exhaust recirculation valve is fully opened (normal range), and power consumption cannot be sufficiently saved. There was a problem. Furthermore, the excessive holding current in the normal range causes the coil temperature to rise in the steady state, which may cause motor out-of-step at the transition from the steady state to the transient state.
Moreover, the reliability of the coil was also lowered.

On the other hand, the drive frequency is set to a relatively low value in order to ensure the required torque even when fully opened and to avoid frequent reverse drive, so that out-of-step can be prevented but is good. There was a problem that it was not possible to obtain excellent responsiveness. For example, during acceleration, the demand for the exhaust gas recirculation amount increases as the intake air amount increases, while the differential pressure between the upstream and downstream of the exhaust gas recirculation valve decreases, so the target opening degree of the exhaust gas recirculation valve increases rapidly. However, if the drive frequency is kept low to prevent motor out-of-step when fully opened as described above, the drive frequency becomes the rate-determining factor and a response delay occurs in the change in the degree of opening of the exhaust gas recirculation valve. There was a fear that the exhaust gas recirculation amount would be insufficient and the NOx amount would increase.

Generally, the target opening degree of the exhaust gas recirculation valve is calculated on the basis of the engine load and the engine speed in time synchronization.
Even if the exhaust gas recirculation valve opening is the same, the exhaust gas recirculation amount tends to decrease as the pressure difference between the upstream and downstream of the exhaust gas recirculation valve decreases, in other words, as the engine load increases, the target opening The degree shows that, when the rotation speed is constant, the load increases exponentially as the load increases.

However, since the driving frequency of the step motor is suppressed to be relatively low as described above, a delay occurs in the opening operation of the exhaust gas recirculation valve, and as shown in FIG. 22, the exhaust gas recirculation amount is insufficient due to the delay. It expands every time and then gradually converges to the target opening. Therefore, this is not a big problem in the initial stage of acceleration when the exhaust gas recirculation amount is relatively small, but in the mid-acceleration period when the exhaust gas recirculation amount becomes the largest, knocking suddenly increases and the drivability deteriorates. There is a problem that the exhaust property is deteriorated (NOx amount is increased). Similarly, at the time of deceleration, there is a delay in the reduction change of the exhaust gas recirculation amount, and the exhaust gas recirculation amount becomes excessive, which causes a misfire, which causes front-rear vibration of the vehicle and an increase in the HC amount. was there.

As described above, conventionally, in order to reliably prevent the occurrence of step-out, the drive frequency is fixed to a relatively low level, and
Since it was fixed to a relatively high holding current, good responsiveness could not be obtained, and power consumption could not be sufficiently suppressed. The present invention has been made in view of the above problems, and by optimally controlling the drive frequency and the holding current of the step motor, the responsiveness of the exhaust gas recirculation amount control and the step-out prevention of the motor are compatible at a high level. The purpose is to let.

[0016]

Therefore, an exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 1 is provided with an exhaust gas recirculation valve in an exhaust gas recirculation path for recirculating a part of exhaust gas to an intake pipe. Is configured to be driven by a step motor to adjust the exhaust gas recirculation amount, and is configured as shown in FIG.

In FIG. 1, the differential pressure detecting means detects the differential pressure between the upstream and downstream of the exhaust gas recirculation valve. The control means based on the differential pressure increases the drive frequency of the step motor as the differential pressure detected by the differential pressure detection means is smaller. The exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 2 is configured as shown in FIG.

In FIG. 2, the coil temperature detecting means detects the coil temperature of the step motor. Then, the coil temperature control means increases the holding current supplied to the step motor when the exhaust gas recirculation valve is stopped in response to an increase in the coil temperature detected by the coil temperature detection means, and the coil temperature detection means. At least one of the control for decreasing the drive frequency of the step motor is performed in accordance with the increase in the coil temperature detected in.

In the exhaust gas recirculation control device for an internal combustion engine according to a third aspect of the invention, the coil temperature detecting means indirectly detects the coil temperature based on the opening degree of the exhaust gas recirculation valve and the valve opening time. And Further, in the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 4, the coil temperature detection means estimates a stationary coil temperature based on an opening of the exhaust gas recirculation valve and an engine load. The estimating means and the coil temperature estimated by the steady-state temperature estimating means are subjected to a smoothing process, and the smoothed coil temperature is calculated as
Finally, a coil temperature anneal processing unit that outputs the detected value of the coil temperature is included.

On the other hand, the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 5 is constructed as shown in FIG. In FIG. 3, the opening degree detection means detects the opening degree of the exhaust gas recirculation valve. The control means based on the opening degree controls the opening degree detection means to increase the holding current supplied to the step motor when the exhaust gas recirculation valve is stopped according to the increase in the opening degree detected by the opening degree detection means. At least one of the control for decreasing the drive frequency of the step motor is performed in accordance with the increase in the opening degree detected in.

An exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 6 is constructed as shown in FIG. In FIG. 4, the differential pressure detecting means detects the differential pressure between the upstream and downstream of the exhaust gas recirculation valve. The basic drive frequency control means sets the basic drive frequency of the step motor to be higher as the differential pressure detected by the differential pressure detecting means is smaller.

On the other hand, the drive frequency correction means corrects the basic drive frequency set by the basic drive frequency control means in accordance with an increase in at least one of the coil temperature of the step motor and the opening degree of the exhaust gas recirculation valve. And set the final drive frequency. In the exhaust gas recirculation control device for the internal combustion engine according to the invention of claim 7, the holding current is adjusted by changing the duty ratio in the chopping control of the current supplied to the step motor.

[0023]

According to the exhaust gas recirculation control device for an internal combustion engine of the first aspect of the present invention, when the pressure difference between the upstream and downstream of the exhaust gas recirculation valve is small, the flow rate sensitivity per step of the step motor becomes low, so the differential pressure The smaller the value is, the higher the drive frequency of the step motor is to ensure the responsiveness, and when the differential pressure is large, the lower the drive frequency is to secure the motor torque to prevent the occurrence of step-out. I chose

According to the exhaust gas recirculation control device for an internal combustion engine according to the second aspect of the present invention, when the coil temperature of the step motor is high, the resistance of the coil increases and the energization current decreases, resulting in a decrease in motor torque. In order to secure the required torque at the time of stop and transition, the holding current is increased and the drive frequency is decreased as the coil temperature is higher, and the power consumption is suppressed while securing the required torque. I tried to get maximum responsiveness.

According to the exhaust gas recirculation control device for an internal combustion engine according to the third aspect of the invention, the coil temperature of the step motor is not directly detected but the coil is determined based on the opening degree of the exhaust gas recirculation valve and the valve opening time. Estimate the heat reception and heat dissipation of
Indirectly detects coil temperature. According to the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 4, the coil temperature in the steady state is estimated based on the opening degree of the exhaust gas recirculation valve and the engine load, while the coil temperature in the steady state is set in the transient state. On the other hand, since the actual coil temperature changes due to the response delay, the coil temperature in the steady state is rounded so that the estimated temperature shows a change commensurate with the response delay.

According to the exhaust gas recirculation control device for an internal combustion engine of the fifth aspect of the present invention, when the opening degree of the exhaust gas recirculation valve is large, the urging force in the valve closing direction is correspondingly large and the required motor torque is increased. As the opening degree of the exhaust gas recirculation valve is increased, the holding current is increased and / or the drive frequency is decreased, so that the required torque is secured and the power consumption is suppressed and the responsiveness is secured.

According to the exhaust gas recirculation control device for an internal combustion engine of the sixth aspect of the present invention, the basic value of the drive frequency is set so that the motor torque required from the differential pressure is secured, while the coil temperature rises and In order to cope with the increase in the required torque due to the increase in the opening degree, the basic drive frequency is corrected, and the step motor is driven based on the corrected drive frequency.

According to the exhaust gas recirculation control device for an internal combustion engine of the seventh aspect of the present invention, the holding current when the exhaust gas recirculation valve is stopped is changed by changing the duty ratio when the energization current to the step motor is chopping controlled. adjust.

[0029]

Embodiments of the present invention will be described below. Figure 5
FIG. 22 is a diagram showing a system configuration of an embodiment, the same elements as those in FIG. 21 are designated by the same reference numerals, and the description thereof will be omitted. Here, the system configuration shown in FIG. 5 is different from the configuration shown in FIG. 21 in that a differential pressure sensor 18 (differential pressure detecting means) and a coil temperature sensor 19 are provided.
The only difference is that (coil temperature detecting means) is added.

The differential pressure sensor 18 is a sensor for detecting the differential pressure between the upstream and downstream of the exhaust gas recirculation valve 5, and the coil temperature sensor 19 is a sensor for detecting the temperature of the coil of the step motor 6. . Then, in the present embodiment, the exhaust gas recirculation valve 5 is drive-controlled as shown in the flowcharts of FIGS. 6 to 8 to adjust the exhaust gas recirculation amount.

In this embodiment, the control means based on the differential pressure, the control means based on the coil temperature, the control means based on the accuracy,
As shown in the flow charts of FIGS. 6 to 8, the engine control computer 8 has software functions of the basic drive frequency control means and the drive frequency correction means. The flowcharts of FIGS. 6 and 7 are routines for calculating the target opening degree of the exhaust gas recirculation valve 5, and are executed every 10 msec.

First, in S1, the cooling water temperature Tw detected by the water temperature sensor 11 and the signal of the idle switch 13 are read. At S2, the read current cooling water temperature T
It is determined whether w exceeds the preset allowable recirculation (EGR) water temperature. When the current cooling water temperature Tw exceeds the predetermined water temperature, the process further proceeds to S3, and it is determined whether or not the idle switch 13 is OFF and the throttle valve 12 is open in the non-idle operation state.

When the idle switch 13 is off and the engine is not idle, the engine speed Ne and the intake air amount Tp are determined in S4.
Read. It should be noted that the intake air amount Tp is the intake air flow rate Q detected by the air flow meter 9 and the engine rotation speed Ne.
Is a value calculated as Tp = K × Q / Ne (K is a constant) based on the above, and is a value representing the engine load.

At S5, the current engine rotation speed is referred to by referring to a map in which the target opening degree of the exhaust gas recirculation valve 5 is stored in advance for each operation range divided by the engine rotation speed Ne and the intake air amount Tp. A target opening degree corresponding to the speed Ne and the intake air amount Tp is searched. On the other hand, if it is determined in S2 that the temperature is lower than the allowable water temperature, or in S3, the idle switch 13 is turned off.
If it is determined to be N, the process proceeds to S6 to read a preset target opening degree when the exhaust gas recirculation is stopped.

At S7, the target opening degree set as described above is stored as STA. In step S8, the differential pressure EBDLTP detected by the differential pressure sensor 18 is read. In S9,
A table in which the basic value of the drive frequency in the drive control of the step motor 6 is stored in advance according to the differential pressure EBDLTP is referred to, and the basic frequency corresponding to the current differential pressure EBDLTP is searched.

In the exhaust gas recirculation valve 5 using the step motor 6 as an actuator, the exhaust gas recirculation amount sensitivity per step becomes smaller as the differential pressure becomes lower. Therefore, the table of the fundamental frequency is shown in FIG. Pressure EBD LTP
The lower the value of, the higher the fundamental frequency is set. As a result, the responsiveness of the exhaust gas recirculation amount control is ensured, and when the differential pressure is large, the drive frequency is kept relatively low to secure the required motor torque, and the occurrence of step-out can be avoided.

When the exhaust recirculation valve 5 is controlled to a low opening and the intake air amount is small and the differential pressure is high, the target opening is likely to oscillate largely due to intake pulsation and rotational fluctuation. If the drive frequency is suppressed to be lower as the pressure is higher, the step motor drive is practically skipped for the oscillation of the target opening, and the occurrence of step-out due to frequent reverse drive can be avoided.

In S10, the basic frequency is stored as DRBSE and the current opening degree of the exhaust gas recirculation valve 5 is loaded as SMON. The opening degree SMON may be a value directly detected by a lift sensor (opening degree detection means) provided in the exhaust gas recirculation valve 5 or may be a control value of the step motor 6 (opening degree). Detection means).

In S11, the coil temperature Tc detected by the coil temperature sensor 19 is read. In S12, the opening SMON
Based on the coil temperature Tc and the coil temperature Tc, reference is made to a map (see FIG. 10) in which the holding current supplied to the step motor when the exhaust gas recirculation valve 5 is stopped is referred to, and the current opening SMON and the coil temperature Tc are corresponded to. Search for holding current. Incidentally, in the present embodiment, since the power consumption is reduced by controlling the energization current of the step motor at the time of stop, the holding current is given as the duty ratio (holding duty) in the chopping control. There is.

As shown in FIG. 10, the map of the holding current (duty ratio) is set to be larger as the coil temperature Tc is higher and larger as the opening SMON is larger. This is because when the coil temperature Tc is high, the resistance of the coil increases and the current flow decreases.
This is because the motor torque is reduced as a result, and in order to secure the motor torque when the coil temperature Tc is high while suppressing the current consumption when the coil temperature Tc is relatively low, the holding current increases as the coil temperature Tc increases. Is designed to be high.

Further, when the opening degree of the exhaust gas recirculation valve 5 is large, the biasing force of the coil spring 7 in the valve closing direction is increased correspondingly, and the required motor torque is increased. Therefore, the holding current increases as the opening degree increases. In addition, securing the required torque and suppressing the current consumption are both achieved. In S13, the holding current (duty ratio) set based on the coil temperature Tc and the opening degree SMON as described above is stored.

At S14, the opening SMON and the coil temperature Tc are set.
Based on the above, the correction value for correcting the basic frequency and setting the final drive frequency is set. The correction value is stored in a map in advance according to the opening degree SMON and the coil temperature Tc, and as shown in FIG.
A correction value for correcting the basic frequency to be smaller is set as c is higher, and a correction value for correcting the basic frequency to be smaller as the opening SMON is set.

In the exhaust gas recirculation valve 5 using the step motor 6 as an actuator, the higher the drive frequency is, the smaller the drive torque is, but the responsiveness is improved. Conversely, when the drive frequency is low, the drive torque is increased. However, the responsiveness deteriorates, so the drive frequency is set lower in order to secure the drive torque at high opening when the required drive torque becomes large, and at the high coil temperature when the generated torque decreases, but at a relatively low opening. When the coil temperature is low and the coil temperature is low, the drive frequency is increased to obtain high responsiveness.

According to the present embodiment, when the coil temperature is low, the drive frequency is set relatively high, and as shown in FIG. 12, the opening of the exhaust gas recirculation valve 5 is set with good response to the change in the target opening. Therefore, it is possible to prevent the shortage of the recirculated exhaust gas amount from increasing with the lapse of time during acceleration so that exhaust performance and drivability are greatly deteriorated. On the other hand, when the coil temperature is high, the drive frequency can be suppressed to the extent that step out does not occur, and as shown in FIG. 13, the occurrence of step out due to a decrease in generated torque can be avoided. Therefore, both responsiveness and reliability (prevention of step-out) can be achieved without increasing the size of the step motor.

In the normal use range, the coil temperature does not greatly increase due to cooling by the running wind. Therefore, even if the drive frequency is suppressed to a low value as the coil temperature rises as described above, the coil temperature is actually low. Is capable of exhibiting good responsiveness in a normal range. In S15, the fundamental frequency DRBSE is multiplied by the correction value retrieved from the map in S14, and the multiplication result is set as the final drive frequency.

In S16, the frequency division number (frequency division period) of the drive routine shown in the flowchart of FIG. 8 to be described later is calculated based on the final drive frequency thus set. S17
Then, the frequency division number (frequency division cycle) is temporarily saved and the present routine is ended. Next, the drive routine shown in the flowchart of FIG. 8 will be described.

This drive routine is executed every 4 msec. First, in S21, the value of the timer for counting the number of frequency divisions is read. In S22, the division timer is set to 0.
If it is not zero, the process proceeds to S23, the value of the frequency division timer is set to decrease, and S
At 24, the timer value after the reduction setting is stored.

On the other hand, if it is determined in S22 that the frequency division timer is 0, the process proceeds to S25, in which the frequency division number (frequency division period) temporarily saved in S17 of the flowchart of FIG. 7 is divided. Set to timer. That is, the routine shown in the flowchart of FIG. 8 is started every 4 msec, but the process proceeds from S22 to S25 every driving cycle corresponding to the driving frequency.

In S26, the target opening degree of the exhaust gas recirculation valve 5 is read. In S27, it is determined whether the target opening and the actual opening match. If the actual opening does not match the target, the duty ratio of the motor output port (PWM port) is set to 100% in S28, and then the magnitude relationship between the actual opening and the target opening is set in S29. The drive output process for the step motor 6 is performed in accordance with the above, and the opening after output is updated as the current opening in S30, and this routine ends.

On the other hand, if the actual opening degree matches the target,
When stopping the opening degree of the exhaust gas recirculation valve 5 at the current position,
In S31, the duty ratio corresponding to the holding current set in the flow charts of FIGS. 6 and 7 is transferred as the motor output duty, and in the next S32, the duty ratio is set in the PWM port of the output phase finally excited. Then, the energization of the step motor 6 is controlled by chopping.

The PWM port is an output port for controlling the ON / OFF of the output based on the internal clock without depending on the time synchronization or the rotation synchronization calculation of the control routine, and controls the excitation of the step motor by the PWM port. By doing so, switching control during driving (duty ratio = 100%) and chopping control during stop (duty ratio = arbitrary) can be performed.

It should be noted that, without using the PWM port, as shown in FIG.
ON / OFF of the output port while monitoring the time with the time synchronization routine whose execution cycle is shorter than that of the drive routine
You may switch. Next, a second embodiment of the target opening calculation routine executed in place of the target opening calculation routine shown in the flowcharts of FIGS. 6 and 7 will be described with reference to the flowcharts of FIGS. 14 and 15.

In the flowcharts of FIGS. 14 and 15,
The target opening degree setting process in S41 to S47 is performed in the same manner as S1 to S7 in the flowchart of FIG. At S48, the engine speed Ne
And map the fundamental frequency based on the intake air amount Tp (Fig.
Search (see 16). Similar to the first embodiment, the fundamental frequency is set to a higher frequency when the pressure difference between the upstream and downstream of the exhaust gas recirculation valve 5 is smaller. However, in the second embodiment, the differential pressure is set to the higher value. Is estimated from the engine rotation speed Ne and the intake air amount Tp, and an appropriate fundamental frequency is set for the differential pressure.

That is, if the engine speed Ne is constant, the differential pressure between the upstream and downstream of the exhaust gas recirculation valve 5 is approximately the intake air amount T.
It is inversely proportional to p and is proportional to the engine speed Ne if the intake air amount Tp (engine load) is constant.
The basic frequency corresponding to the differential pressure can be set based on e and the intake air amount Tp, and the differential pressure sensor 18 can be omitted by eliminating the need to directly detect the differential pressure. It should be noted that, as in the first embodiment, the characteristic is that the fundamental frequency is set lower as the differential pressure is larger.

At S49, the basic frequency set based on the engine speed Ne and the intake air amount Tp is stored, and the current opening degree of the exhaust gas recirculation valve 5 is loaded. In S50, based on the current opening degree of the exhaust gas recirculation valve 5, a table of temperature rising gradient values used for estimating the coil temperature is displayed (see FIG. 17).
Search from. The temperature rise gradient value is given as a positive or negative value representing the amount of heat received and the amount of heat radiated in the coil of the step motor, and is 0 at a predetermined opening,
In an area where the opening is smaller than the predetermined opening, a negative value that the absolute value increases as the opening decreases is set, and in an area where the opening is larger than the predetermined opening, the absolute value increases as the opening increases. Is set to a positive value.

This corresponds to the fact that the amount of recirculated exhaust gas is small below the predetermined opening amount, so that heat is radiated, while the amount of exhaust gas recirculation is relatively large above the predetermined opening amount, and heat is received by the coil. are doing. In S51, the temperature rise gradient value is added to the estimated temperature counter, and the heat reception amount and the heat radiation amount for each time are integrated to estimate the coil temperature based on the opening degree and the valve opening time.

In S52, it is judged whether or not the estimated coil temperature Tc is lower than the maximum value. If it is higher than the maximum value, the estimated temperature Tc is reset to the maximum value in S53.
Further, in S54, it is judged whether or not the estimated coil temperature Tc exceeds the minimum value.
In step S55, the estimated temperature Tc is reset to the minimum value, and the estimated temperature Tc is limited to the preset maximum and minimum values.

In the next steps S56 to S61, the holding current (duty ratio) is set based on the estimated coil temperature Tc as in steps S12 to S17 in the flowchart of FIG. Is set, and the final drive frequency is determined according to the correction value. Next, a third embodiment of the target opening degree calculation routine will be described with reference to the flowcharts of FIGS. 18 and 19.

In the flowcharts of FIGS. 18 and 19,
Since the target opening degree setting process and the basic frequency setting in S71 to S79 are performed in the same manner as S41 to S49 in the flowcharts of FIGS. 14 and 15, description thereof will be omitted. In S80 (steady-state temperature estimating means), the current opening and intake air amount are calculated from a map (see FIG. 20) in which the coil temperature in steady state is stored in advance according to the opening and the intake air amount Tp (engine load). Find the coil temperature corresponding to Tp.

The coil temperature map is obtained by previously measuring the coil temperature in a steady state determined by the opening degree and the engine load and storing the data in the map. Next S
In 81 (coil temperature smoothing processing means), the retrieved normal coil temperature is weighted averaged by a coefficient A (0 <A <1) determined by the heat capacity of the exhaust gas recirculation valve 5 and the like. Specifically, the current estimated temperature Tc is calculated by performing a weighted average (moving average) of the previous estimated temperature Tco and the steady-state temperature Tc retrieved from the current map according to the following formula.

Tc = A × Tco + (1−A) × Tc The coil temperature corresponding to the steady state is subjected to the above-mentioned weighted average smoothing process to delay the response to changes in the opening and engine load. Therefore, the coil temperature can be accurately estimated according to the changing coil temperature. S82 ~
In S85, similarly to S52 to S55 in the flow charts of FIGS. 14 and 15, a process of limiting the estimation result of the coil temperature to predetermined maximum and minimum values is performed.

In S86, the weighted average result of this time is saved as the previous value Tco so as to be used in the weighted average calculation in S81 at the next execution of this routine. Below, S87
In S92, the holding current (duty ratio) is determined using the estimated coil temperature in the same manner as in S56 to S61 in the flowcharts of FIGS. 14 and 15, and
A final drive frequency is calculated by setting a drive frequency correction value.

[0063]

As described above, according to the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 1, the driving frequency of the step motor is made higher as the differential pressure between the upstream and downstream of the exhaust gas recirculation valve is smaller. Therefore, when the differential pressure at which the flow rate sensitivity per step of the step motor is low is small, responsiveness can be secured by setting a high drive frequency, and when the differential pressure is large, the drive frequency is kept relatively low and the required torque is reduced. There is an effect that it is possible to generate.

According to the exhaust gas recirculation control device for an internal combustion engine of the second aspect of the present invention, the holding current is increased and the drive frequency is decreased when the coil temperature of the step motor is high and the motor torque is reduced. Therefore, there is an effect that the required torque is secured, the power consumption is suppressed, and the maximum responsiveness is obtained. According to the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 3, the heat reception and the heat radiation of the coil are estimated based on the opening degree of the exhaust gas recirculation valve and the valve opening time, and thus the coil temperature is indirectly detected. Therefore, there is an effect that it is not necessary to provide a dedicated temperature sensor.

According to the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 4, the coil temperature in the steady state estimated based on the opening degree of the exhaust gas recirculation valve and the engine load is subjected to the smoothing process. Therefore, there is an effect that the coil temperature can be accurately estimated in accordance with the response delay of the coil temperature change. According to the exhaust gas recirculation control device for an internal combustion engine according to the invention of claim 5, the holding current is increased and / or the drive frequency is decreased as the opening degree of the exhaust gas recirculation valve is increased. When the degree is large and the urging force in the valve closing direction is large, it is possible to obtain the required torque, while suppressing the power consumption and ensuring the responsiveness.

According to the exhaust gas recirculation control device for an internal combustion engine of the sixth aspect of the present invention, by setting the basic value of the drive frequency in accordance with the differential pressure between the upstream and downstream of the exhaust gas recirculation valve, it is necessary to secure responsiveness and Correcting the basic frequency according to the coil temperature and the opening while achieving compatibility with securing the torque has the effect that it is possible to cope with an increase in the required torque due to an increase in the coil temperature and an increase in the opening. is there.

According to the exhaust gas recirculation control device for an internal combustion engine of the seventh aspect of the invention, the duty ratio is changed when chopping the energizing current to the step motor to change the duty ratio, thereby suppressing the power consumption and reducing the exhaust gas recirculation valve. There is an effect that the holding current at the time of stop can be adjusted.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an exhaust gas recirculation control device according to a first aspect of the invention.

FIG. 2 is a basic configuration diagram of an exhaust gas recirculation control device according to a second aspect of the invention.

FIG. 3 is a basic configuration diagram of an exhaust gas recirculation control device according to a fifth aspect of the invention.

FIG. 4 is a basic configuration diagram of an exhaust gas recirculation control device according to a sixth aspect of the invention.

FIG. 5 is a system configuration diagram of an embodiment.

FIG. 6 is a flowchart showing a target opening calculation routine of the first embodiment.

FIG. 7 is a flowchart showing a target opening calculation routine of the first embodiment.

FIG. 8 is a flowchart showing a drive output routine of the embodiment.

FIG. 9 is a diagram showing a characteristic of a fundamental frequency according to a differential pressure.

FIG. 10 is a diagram showing characteristics of a holding current according to an opening and a coil temperature.

FIG. 11 is a diagram showing a characteristic of a frequency correction value according to an opening and a coil temperature.

FIG. 12 is a diagram for explaining control characteristics when the coil temperature is low.

FIG. 13 is a diagram for explaining control characteristics when the coil temperature is high.

FIG. 14 is a flowchart showing a target opening calculation routine of the second embodiment.

FIG. 15 is a flowchart showing a target opening calculation routine of the second embodiment.

FIG. 16 is a diagram showing characteristics of a fundamental frequency according to a rotation speed and an intake air amount.

FIG. 17 is a diagram showing a characteristic of a temperature rise gradient value according to an opening degree.

FIG. 18 is a flowchart showing a target opening calculation routine of the third embodiment.

FIG. 19 is a flowchart showing a target opening calculation routine of the third embodiment.

FIG. 20 is a diagram showing a characteristic of a coil temperature in a steady state according to an opening degree and an intake air amount.

FIG. 21 is a system configuration diagram of a conventional exhaust gas recirculation device.

FIG. 22 is a diagram for explaining problems of the conventional exhaust gas recirculation device.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Intake Manifold 3 Exhaust Manifold 4 Exhaust Circulation Route 5 Exhaust Recirculation Valve 6 Step Motor 7 Coil Spring 8 Engine Control Computer 9 Air Flow Meter 10 Crank Angle Sensor 11 Water Temperature Sensor 12 Throttle Valve 13 Idle Switch 18 Differential Pressure Sensor 19 Coil Temperature Sensor

Claims (7)

[Claims] 1. An exhaust gas recirculation control apparatus for an internal combustion engine, comprising an exhaust gas recirculation valve in an exhaust gas recirculation path for recirculating a part of exhaust gas to an intake pipe, and controlling the exhaust gas recirculation amount by driving the exhaust gas recirculation valve with a step motor. In the above, the differential pressure detection means for detecting the differential pressure between the upstream and downstream of the exhaust gas recirculation valve, and the differential pressure control for increasing the drive frequency of the step motor as the differential pressure detected by the differential pressure detection means is smaller. An exhaust gas recirculation control device for an internal combustion engine, comprising: 2. An exhaust gas recirculation control device for an internal combustion engine, wherein an exhaust gas recirculation valve for recirculating a part of exhaust gas to an intake pipe is equipped with an exhaust gas recirculation valve, and the exhaust gas recirculation valve is driven by a step motor to adjust the amount of exhaust gas recirculation. In the coil temperature detecting means for detecting the coil temperature of the step motor, and the holding current supplied to the step motor when the exhaust gas recirculation valve is stopped is increased according to the increase in the coil temperature detected by the coil temperature detecting means. Control means for controlling the coil temperature and performing at least one of control and control for decreasing the drive frequency of the step motor in response to an increase in the coil temperature detected by the coil temperature detection means. Exhaust gas recirculation control device for internal combustion engine. 3. The exhaust gas recirculation for an internal combustion engine according to claim 2, wherein the coil temperature detecting means indirectly detects the coil temperature based on an opening degree of the exhaust gas recirculation valve and a valve opening time. Control device. 4. The coil temperature detecting means estimates a coil temperature in a steady state based on an opening of the exhaust gas recirculation valve and an engine load, and a steady temperature estimating means. And a coil temperature smoothing means for finally outputting the coil temperature thus smoothed as a detected value of the coil temperature. An exhaust gas recirculation control device for an internal combustion engine according to claim 2. 5. An exhaust gas recirculation control device for an internal combustion engine, wherein an exhaust gas recirculation valve for recirculating a part of exhaust gas to an intake pipe is provided with an exhaust gas recirculation valve, and the exhaust gas recirculation valve is driven by a step motor to adjust the amount of exhaust gas recirculation. In the opening degree detecting means for detecting the opening degree of the exhaust gas recirculation valve, and the holding current supplied to the step motor when the exhaust gas recirculation valve is stopped is increased according to the increase in the opening degree detected by the opening degree detection means. Control for controlling the step motor and at least one of the control for decreasing the drive frequency of the step motor in response to the increase in the opening detected by the opening detection means. Exhaust gas recirculation control device for internal combustion engine. 6. An exhaust gas recirculation control device for an internal combustion engine, wherein an exhaust gas recirculation valve for recirculating a part of exhaust gas to an intake pipe is equipped with an exhaust gas recirculation valve, and an exhaust gas recirculation amount is adjusted by driving the exhaust gas recirculation valve with a step motor. In the above, the differential pressure detecting means for detecting the differential pressure between the upstream and downstream of the exhaust gas recirculation valve, and the basic drive for setting the basic drive frequency of the step motor higher as the differential pressure detected by the differential pressure detecting means is smaller. Frequency control means, and final drive by correcting the basic drive frequency set by the basic drive frequency control means in accordance with an increase in at least one of the coil temperature of the step motor and the opening degree of the exhaust gas recirculation valve. An exhaust gas recirculation control device for an internal combustion engine, comprising: a drive frequency correction unit that sets a frequency. 7. The exhaust gas of an internal combustion engine according to claim 2, wherein the holding current is adjusted by changing a duty ratio in chopping control of a current supplied to a step motor. Reflux control device.