JPH0771295A - Stability control device for engine - Google Patents

Abstract

PURPOSE:To prevent an air-fuel ratio from being controlled to lean condition by mistake at the time of non lock up condition in an A/T car or at the time of non-contact condition of a clutch in a M/T car. CONSTITUTION:Stability of an engine is detected from rotation fluctuation of the engine by a detecting means 31. When it is judged by a judging means 32 whether an operating condition signal is in lean condition or not, a value of lean side more than theoretical air-fuel ratio is set as a target air-fuel ratio by a control means 33 in lean condition by the judging result, and also feedback control of the air-fuel ratio is carried out so as to match the detecting value of stability with a prescribed stability target value. When it is judged by a judging means 34 that an engine and a vehicle driving system are in not directly connecting condition, feedback control of the air-fuel ratio is exhibited by an exhibiting means 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stability control device for an engine, and more particularly to a device for detecting a fluctuation in engine rotation and performing feedback control of an air-fuel ratio and an exhaust gas recirculation amount of a lean burn engine so that the fluctuation falls within an allowable level.

[0002]

2. Description of the Related Art With a lean air-fuel ratio, the amount of air is large to generate the same torque as the stoichiometric air-fuel ratio but the pumping loss is reduced, and the lean air-fuel ratio has a larger specific heat ratio of combustion gas. The fuel efficiency is improved by operating with the lean air-fuel ratio, and NOx is originally low in the lean air-fuel ratio. Therefore, there is a method in which the lean-side air-fuel ratio is used as a target value under a certain condition to perform feedback control of the air-fuel ratio. (See Japanese Patent Laid-Open No. 2-27232).

To explain this, combustion tends to become unstable under lean conditions, and a surge occurs due to this unstable combustion, so the target under lean conditions is such that the surge torque level approaches the stability limit level. The air-fuel ratio must be set. However, when the air-fuel ratio shifts to the lean side due to variations in the characteristics of the fuel injection valve and the air flow meter, changes over time, etc., the surge torque exceeds the stable limit, and conversely when it shifts to the rich side, fuel economy is not improved, NOx also increases.

Therefore, the surge torque level is estimated from the revolution speed signal in the lean air-fuel ratio range, and the air-fuel ratio is feedback-controlled so that the surge torque level approaches the stable limit level, resulting in variations in fuel injection valves and air flow meters. Even if the environmental conditions change, the fuel consumption is improved and NOx is reduced while maintaining the surge torque level close to the stability limit level.

Further, during acceleration / deceleration, the above-mentioned feedback control is prohibited to prevent erroneous detection of torque fluctuation due to rotation fluctuation during acceleration / deceleration as surge torque.

[0006]

By the way, after a surge occurs in a vehicle due to instability of combustion, stability control is performed in a direction to stabilize combustion. It does not stop immediately, and vehicle surge may continue even after the combustion itself stabilizes. In such a case, it is necessary to control the combustion to be more stable until the surge of the vehicle is suppressed.

However, when the engine and the vehicle are not directly connected, control is performed only by the combustion stability of the engine regardless of the surge of the vehicle.

[0008] For example, a torque converter that constantly transmits power by means of a fluid by means of a torque converter always causes a slight slip, which causes the fuel consumption of an A / T vehicle (a vehicle with an automatic transmission). A so-called lock-up mechanism that directly connects the input shaft and the output shaft of the torque converter is provided because it leads to badness, and the lock-up mechanism works in a lock-up region such as during high-speed traveling. In this case, from lock-up to non-lock-up, where the influence of the vehicle on engine speed fluctuations (due to the acceleration in the longitudinal direction of the vehicle) is large, the detected engine speed fluctuations are the same, even though the vehicle stability is the same. Therefore, the air-fuel ratio is erroneously judged to be lean even though the stability of the vehicle is not changed to be improved.

Similarly, even in the case of an M / T vehicle (which means a vehicle with a manual transmission), it is erroneously determined that the vehicle has changed to a stable side even when the engine rotation is stabilized by idling.

Therefore, the present invention determines whether or not the engine and the drive system of the vehicle are in the non-direct connection state, and prohibits the feedback control of the stability in the non-direct connection state.
An object of the present invention is to prevent an erroneous determination from occurring when the A / T vehicle is not locked up and the M / T vehicle is not engaged with the clutch.

[0011]

As shown in FIG. 1, a first aspect of the present invention is a means 31 for detecting the stability of an engine from fluctuations in the rotation of the engine, and determining whether an operating condition signal is a lean condition. Means 32 for controlling the air-fuel ratio to a target air-fuel ratio leaner than the theoretical air-fuel ratio under a lean condition based on the determination result, and feedbacking the air-fuel ratio so that the stability detection value matches a predetermined stability target value. A control means 33, a means 34 for determining whether or not the engine and the vehicle drive system are in a non-direct connection state, and a means 35 for prohibiting the feedback control of the air-fuel ratio in the non-direct connection state based on the result of the determination are provided. It was

The second invention, as shown in FIG. 24, is the first invention.
In the invention, the feedback control means 33 is
Target air-fuel ratio Md on the lean side of the theoretical air-fuel ratio under lean conditions
means 41 for calculating ml, and the air-fuel ratio correction amount Lldm so that the detected value of the stability matches a predetermined stability target value.
means 42 for calculating 1 and this air-fuel ratio correction amount Lldml
Means 43 for correcting the target air-fuel ratio Mdml under the lean condition, and the fuel injection amount is calculated based on the corrected target air-fuel ratio Tdml (for example, the basic injection amount Tp at which the theoretical air-fuel ratio can be obtained is calculated as follows). Means 44 for calculating the fuel injection amount by correcting the basic injection amount Tp with the corrected target air-fuel ratio Tdml and calculating the fuel injection amount according to the detected values of the load and the rotational speed. And a means 45 for supplying

A third aspect of the present invention, as shown in FIG. 25, means 3 for detecting the stability of the engine from fluctuations in the engine rotation.
1, a means 51 for determining whether or not the operating condition signal is an EGR condition, a value corresponding to the operating condition signal under the EGR condition is set as a target EGR rate based on the result of the determination, and the stability detection value is predetermined. Means 52 for performing feedback control of the EGR rate so as to match the stability target value, means 34 for determining whether the engine and the drive system of the vehicle are in the non-direct connection state, and the non-direct connection state based on the result of this determination. Therefore, means 53 for prohibiting the feedback control of the EGR rate is provided.

The fourth aspect of the present invention is, as shown in FIG.
In the invention, the feedback control means 72 is
Target EGR rate MEG according to operating condition signal under EGR condition
A means 61 for calculating R and an EGR rate correction amount LlEG so that the detected value of the stability coincides with a predetermined stability target value.
Means 62 for calculating R, and this EGR rate correction amount LlEG
It comprises means 63 for correcting the target EGR rate MEGR under the EGR condition with R, and means 64 for controlling the opening degree of the flow control valve in the EGR passage based on the corrected target EGR rate TEGR.

In a fifth aspect of the present invention, in any one of the first to fourth aspects, the uncoupled state determination means 34 includes a sensor 71 for detecting an engine speed and a gear position of a transmission. A sensor 72 for detecting, a means 73 for calculating a vehicle speed predicted value VSPe from the detected values of the gear position and the engine speed, a sensor 74 for detecting an actual vehicle speed, the actual vehicle speed VSP and the vehicle speed predicted value VSPe. By comparison, when the absolute value of the difference between the two exceeds a predetermined value β, the unit 75 determines that it is in the non-direct connection state.

[0016]

When the feedback control of the air-fuel ratio is performed so that the detected value of the stability of the engine matches the target value of the stability, with the value on the lean side of the stoichiometric air-fuel ratio as the target air-fuel ratio under the lean condition, the fuel injection valve is operated. In spite of variations in airflow meters and airflow meters, and changes in environmental conditions (such as changes in intake air temperature and humidity), while maintaining the detected stability value of the engine at the stability target value, improve fuel efficiency and reduce NOx emissions as in the past. It can be reduced.

On the other hand, in the A / T vehicle, the rotational fluctuation is smaller when the lockup is not performed (non-directly connected state) than when the lockup is (directly connected state), and in the M / T vehicle, the clutch is not connected (or half-clutch). Rotation fluctuation may be smaller than when the clutch is connected (directly connected state), and if feedback control is performed in the same manner as in the direct connected state even in these non-locked-up states, such as when the lockup is not performed and the clutch is not connected, The stability is not changed, but the air-fuel ratio is erroneously controlled to the lean side, and the drivability deteriorates when returning to the direct connection state.However, feedback control is performed when the non-direct connection state is determined in the first invention. Is prohibited, it is possible to avoid erroneously controlling the air-fuel ratio to the lean side in the non-direct connection state. As a result, the drivability immediately after returning to the direct connection state is not deteriorated even if there is a decrease in the rotation fluctuation due to the direct connection between the engine and the vehicle drive system.

In the second aspect of the present invention, the target air-fuel ratio Mdml under the lean condition is corrected by the air-fuel ratio correction amount Lldml calculated so that the detected value of the engine stability coincides with the target stability value. When the fuel injection amount is calculated based on the target air-fuel ratio, the conventional configuration for feedback control of the air-fuel ratio targeting the theoretical air-fuel ratio and the map used for this control (for example, the map of the target air-fuel ratio under lean conditions) The value of can be used as it is, and the man-hour for creating a map can be reduced.

In an engine equipped with an EGR device that recirculates exhaust gas to the intake pipe, increasing the ratio of EGR gas to fresh air (that is, EGR rate) within a range that does not deteriorate combustion improves fuel efficiency and reduces NOx. Effective, but third
When the feedback control of the EGR rate is performed so that the detected value of the stability of the engine matches the target value of the stability, with the value corresponding to the operating condition signal under the EGR condition as the target EGR rate in the invention of FIG. Optimal EGR regardless of flow rate variations of the flow control valve that controls
In addition to the above, the drivability immediately after returning to the direct connection state is not deteriorated and the EGR rate is incorrect even if there is a decrease in the rotation fluctuation due to the direct connection between the engine and the vehicle drive system. Since it is not controlled, an increase in NOx can be prevented.

In the fourth aspect of the invention, the EGR rate correction amount LlEGR calculated so that the detected value of the engine stability coincides with the target stability value is used to obtain the target EGR rate MEGR corresponding to the operating condition signal under the EGR condition. When the opening degree of the flow control valve in the EGR passage is corrected and the opening degree of the flow control valve in the EGR passage is controlled by the corrected target EGR rate, the conventional configuration for performing the open control of the EGR rate using a value matched in advance according to the operating condition signal It is possible to use the values of the map used for this control as they are.

In the fifth aspect of the invention, the actual vehicle speed VSP and the predicted vehicle speed VSPe are compared with each other, and when the absolute value of the difference between the two exceeds a predetermined value β, it is determined that the vehicle is in a non-direct connection state. Compared to the case of determining the non-direct connection state in the car (that is, non-lockup state) from the lockup signal or the case of determining the non-direct connection state from the amount of depression of the clutch pedal in the M / T vehicle, the clutch deteriorates with time. Even when a large slip occurs, it can be determined that the non-direct connection state is established, and the accuracy of the determination as to whether or not the non-direct connection state is improved.

[0022]

In FIG. 2, the air sucked from the air cleaner 11 is temporarily stored in a collector portion 12a having a constant volume, and then flows into each cylinder through a branch pipe. A fuel injection valve 3 is provided in the intake port 12b of each cylinder, and fuel is intermittently injected from the injection valve 3 in synchronization with engine rotation.

When the injection time from the injection valve 3 is long, the injection amount is large, and when the injection time is short, the injection amount is small. The richness of the air-fuel mixture, that is, the air-fuel ratio, shifts to the rich side when the fuel injection amount for a fixed amount of intake air increases, and shifts to the lean side when the fuel injection amount decreases. Therefore, if the control unit 2 determines the basic injection amount of fuel so that the ratio to the intake air amount becomes a constant value, the same air-fuel ratio can be obtained even under different operating conditions. When the fuel injection is performed once per one revolution of the engine, the basic injection pulse width Tp is calculated from the intake air amount at that time and the engine speed with respect to the air amount sucked in one revolution. Usually, the air-fuel ratio determined by this Tp is near the stoichiometric air-fuel ratio.

When a certain condition is satisfied, the control unit 2 switches the target value of the air-fuel ratio from the stoichiometric air-fuel ratio to the lean-side air-fuel ratio. At this switching, the auxiliary air flow rate is increased (corrected at the time of switching to the stoichiometric air-fuel ratio) so that the torque is controlled to be the same before and after the switching. Therefore, the intake throttle valve 5 is bypassed. A large flow rate control valve 22 is provided in the auxiliary air passage 21. The control valve 22 is of a proportional solenoid type and has an on-duty (O of a fixed cycle) from the control unit 2.
The larger the N time ratio), the larger the auxiliary air flow rate flowing through the passage 21.

In order to suppress CO and HC which increase due to unstable combustion in the lean air-fuel ratio range, the intake port 12b is provided so that swirl is given to the intake air flowing into the combustion chamber.
A swirl control valve 13 having a notch (not shown) in a part is provided in the vicinity of. In the lean air-fuel ratio region, the swirl control valve 13 is fully closed to throttle the intake air to increase the flow velocity of the intake air and generate swirl in the combustion chamber. Exhaust pipe 1 in the stoichiometric air-fuel ratio range
NOx is purified by the three-way catalyst 19 provided in No. 8.

In the lean air-fuel ratio range, the control unit 2 also detects the stability of the engine from the rotational fluctuation, and the air-fuel ratio is adjusted so that the engine stability detection signal matches the slice level (stability target value). The correction amount is updated, and the basic value (map value) of the target air-fuel ratio in the lean air-fuel ratio range is corrected with this correction amount. By this feedback control of stability, the engine is operated at a lean air-fuel ratio that is close to the limit at which the engine does not become unstable, and the fuel efficiency is improved while stabilizing the engine.

However, the stability of the vehicle is improved even when the rotational fluctuation becomes small due to the fact that the engine and the vehicle drive system are not directly connected and there is no influence on the engine rotational fluctuation from the vehicle. Assuming that the air-fuel ratio correction amount is
If you accidentally updated the air-fuel ratio to the lean side,
Immediately after returning to the direct connection state, drivability deteriorates.

To deal with this, the control unit 2 calculates a vehicle speed prediction value from the engine speed and gear position, and compares the absolute value of the difference between the vehicle speed prediction value and the actual vehicle speed with a predetermined value. When the difference between the two exceeds a predetermined value, it is determined that the engine and the drive system of the vehicle are not directly connected,
Prohibit stability feedback control.

Therefore, the signal from the inhibitor switch for detecting the gear position and the signal from the vehicle speed sensor is the signal from the sensor required for stability control (4 is a hot wire type air flow meter for detecting the air amount Qa sucked from the air cleaner). ,
6 is a throttle sensor, 7 is a crank angle sensor that outputs a signal for each unit crank angle and a signal for each reference position of the crank angle, and 8 is a water temperature sensor), and is also input to a control unit 2 including a microcomputer.

Considering that the fuel control is performed aiming at the target air-fuel ratio, and finally the supplied fuel amount is obtained from the detected value of the air flow rate, (air flow rate) × (fuel air ratio) = (supply The fuel-air ratio is easier to handle than the air-fuel ratio because the relationship of the fuel amount) is established. Therefore, the fuel-air ratio is used for some numerical values below.

[1] Calculation of rotational fluctuation Since rotational fluctuation occurs due to instability of combustion, a cycle between REFs (cycle between reference signals REF of crank angle) is measured, and the latest value and the previous cycle of this cycle between REFs are measured. The rotation speed for each cylinder is calculated based on the added value of the values, and the stability of combustion is estimated from the variation in the rotation speed for each cylinder.

In FIG. 4, the cycle Refrv of one engine revolution period is calculated from the cycle REF between REFs, Refrv = Ref + Ref _n-1 (1) where Ref _n-1 ; the previous cycle between REFs (FIG. 4). 21), and Nerv = KN # / Refrv (2) where KN #; cycle-to-rotation speed conversion constant is converted to the cylinder-by-cylinder rotation speed Nerv (step 23 in FIG. 4).

The reason why the formula (1) is derived is as follows. 4-cylinder engine (ignition order # 1- # 3- # 4
FIG. 5 shows the relationship between the combustion pressure and the rotational fluctuation of each cylinder and the reference signal REF (which rises every 180 ° CA) for the (-# 2). Rotational fluctuations due to combustion in each cylinder occur according to the ignition sequence for each 180 ° CA (crank angle of engine half rotation), whereas the reference signal REF is a predetermined crank angle before compression top dead center (TDC in the figure). When rising at (for example, 110 ° CA), one combustion section and the REF cycle of the cylinder in which the combustion is performed are temporally displaced.

If the # 3 cylinder is used as a representative, the rotational fluctuation due to combustion of the # 3 cylinder (from # 3TDC to # 4TDC) spans two cycles of the # 3REF cycle and the # 4REF cycle. The crank angle range in which the combustion of the cylinder contributes is 110 ° CA in the cycle between # 4REF (from the figure to # 4TDC) and 70 ° CA in the cycle between # 3REF (from # 3TDC). is there. Assuming that the contribution ratios are k ₁ and k ₂ , respectively, k ₁ = 110/180 (1.1) k ₂ = 70/180 (1.2), and the half rotation section cycle of the # 3 cylinder is # 3 cylinder half-rotation period cycle = # 4 REF inter-cycle × k ₁ + # 3 REF inter-cycle × k ₂ (1.3)

Here, since the REF period is obtained in the ignition order, if the latest value Ref of the REF period obtained this time in equation (1.3) is associated with the # 4 cylinder, the previous value Ref _{n- of the} REF period is set. _{If 1} corresponds to the # 3 cylinder, and if the # 4 cylinder is considered as the current cylinder (current cylinder), the # 3 cylinder is the previous cylinder (the cylinder one before in the ignition order from the current cylinder). .3) can be rewritten as the half-rotation section cycle of the front cylinder = Ref × k ₁ + Ref _n−1 × k ₂ (1.4).

The equation (1.4) is an equation in which the # 4 cylinder is considered as the current cylinder, but the equation is the same as the equation (1.4) even when the # 2, # 1, and # 3 cylinders are considered as the current cylinder.

The above-mentioned contribution ratios k ₁ and k ₂ are for when combustion starts from TDC (compression top dead center) in each cylinder. Considering that actual combustion starts before TDC, requires correction by the combustion start crank angle, this time in the above (1.1), (1.2) in place of the equation, k ₁ = (110- combustion start crank angle) / 180 ... (1.5) k ₂ = (70 + combustion start crank angle) / 180 (1.6) must be used. For example, assuming that the average value of the combustion start crank angle is 20 ° CA before the compression top dead center, k ₁ = (110-20) /180=0.5 (1.7) k ₂ = (70 + 20) / 180 = 0.5 ... (1.8) Therefore, the equation (1.4) becomes the half rotation section cycle of the previous cylinder = Ref × 0.5 + Ref _n−1 × 0.5 (1.9) .

Since it is actually difficult to know the ignition timing, the ignition timing is adopted as the equivalent value of the above combustion start crank angle.

By doubling both sides of the equation (1.9), one revolution section cycle of the front cylinder = Ref + Ref _n-1 (1.10) This equation (1.10) is the equation (1). is there. That is,
Since Refrv in the equation (1) represents one revolution section cycle of the previous cylinder, the latest value (Ref) of the cycle between REFs is calculated by the equation (1).
By converting the added value of the previous value (Ref _n-1 ) into the rotational speed unit by the equation (2), the rotational speed for each cylinder can be obtained.

When the two REF cycles (current value and previous value of the REF cycle) are shown in FIG. 6 as measurement intervals, the measurement intervals between two cylinders adjacent in the ignition order are as shown in FIG. It shifts while overlapping the measurement section.
When the cylinder-by-cylinder rotational speed is obtained in this way, the rotational fluctuation due to the variation between the cylinders is not mistakenly recognized as the rotational fluctuation due to the unstable combustion.

According to the equation (1.9), k is obtained as a result.
₁ and k ₂ are equal (both are 0.5),
This is <a> In-line 4-cylinder engine <b> REF rises at 110 ° CA before compression top dead center <c> Combustion start crank angle is 20 ° CA before compression top dead center 3 Only when all of the two conditions are satisfied, if any one of these conditions is not satisfied, k ₁ ≠ k ₂ .

From the rotational speed Nev for each cylinder in the above equation (2), Dnerv = Nev-Nev _n-4 (3) where Nev _n-4 ; The rotational change amount Dnerv for each cylinder in the Nev equation four times before. Is calculated (Fig. 4
Step 25).

When the cylinder-by-cylinder rotational speed Nev in the equation (2) is, for example, that of the # 1 cylinder (previous cylinder), Nev
_n-1 (the value one time before) is for # 2 cylinder, Nev _n-2 (the value before two times) is for # 4 cylinder, and Nev _n-3 (the value before three times) is #
Since it has three cylinders, in order to obtain the rotation change amount for the # 1 cylinder, the value four times before (that is, the value one cycle before) must be used in the equation (3). As described above, by obtaining the difference between the latest value of the cylinder-by-cylinder rotational speed and the value one cycle before as the cylinder-by-cylinder rotational change amount Dnerv, the variation between the cylinders is not mistaken for rotational fluctuation due to unstable combustion. That is why.

Before the calculation of the equation (2), the old Nev is shifted (step 22 in FIG. 4). This is an operation of sequentially transferring the data of one rotation before to the RAM of two times before, the data of two rotations before three times, and the data three rotations before four times. Since the engine speed N for each cylinder is stored by the shift of the old Nev, the engine speed N described later
e = Ne = (Nev + Nev _n-1 + Nev _n-2 + Ner
It can be calculated as the average value of the engine speeds of all cylinders by the formula of v _n-3 ) / 4.

The shift of the old Dnerv is similar to the shift of the old Nerv (step 24 in FIG. 4).

From the cylinder-by-cylinder rotational change amount Dnerv, Llj = Dnerv-Dnerv _n-1 (4) where Dnerv _n-1 ; Amount is the torque fluctuation equivalent value L
It is obtained as lj (step 26 in FIG. 4).

Since Dnerv in the equation (3) is the amount of rotation change that has occurred for one cylinder between one rotation cycle at the time of the previous combustion and one rotation cycle at the time of the current combustion, Lnj of the expression (4) is given.
Corresponds to a pseudo torque fluctuation amount due to combustion.

The torque fluctuation equivalent value Llj is subjected to bandpass filter processing, and the result is stored as a digital filter processing output Lljd (steps 27 and 2 in FIG. 4).
8). Since the bandpass filter processing is performed by software, an equation converted from a continuous system to a discrete system is used. The frequency may be a frequency (3 to 7 Hz) that is easily felt by the driver of the vehicle as a surge.

[2] Determining Whether or Not to Perform Stability Feedback Control Under the lean condition, the air-fuel ratio is feedback controlled so that the digital filtering output Lljd, which is the stability signal, matches the slice level (stability target value). However, when fluctuations in rotation occur due to factors other than combustion instability such as during transient operation, and it is mistaken for rotation fluctuation due to unstable combustion, or vehicle stability and engine rotation fluctuation become irrelevant. In such a case, feedback control is prohibited.
Specifically, as shown in FIG. 7, the following <1> to <5>
If any one of the conditions is satisfied, the feedback control prohibition flag is set to "1" (step 3 in FIG. 7).
6). In the figure, feedback is indicated by F / B.

<1> The lean condition is not satisfied (step 31 in FIG. 7). For lean conditions, for example, the cooling water temperature is 80 ° C.
That is, all the conditions that the throttle valve opening from the throttle sensor 6 is less than or equal to a predetermined value and the vehicle speed change is less than or equal to a predetermined value are satisfied.

<2> The air-fuel ratio is being switched (step 32 in FIG. 7). For example, when Dml (a target fuel-air ratio damper value) and Tdml (a target fuel-air ratio map correction value) described later are not the same, it is determined that switching is in progress.

<3> Gear position <predetermined value LLGR # (step 33 in FIG. 5). A larger value is assigned to the higher gear position as the gear position (for example, 1
Feedback control is prohibited when the gear position is <LLGR #, corresponding to the second speed, the third speed, the fourth speed, 1, 2, 3, and 4).
This is because the change in engine speed is fast during low-speed gear running, which causes disturbance to the stability, so that feedback control is prohibited (for example, prohibited at first speed).

<4> The absolute value of the difference between the actual vehicle speed VSP [km / h] and the predicted vehicle speed VSPe [km / h] exceeds the predetermined value β (step 34 in FIG. 7). Predicted vehicle speed VS Pe [km / h] is gear position and engine speed N
The vehicle speed predicted from e [rpm], VSPe = Ne ・ 2 ・ π ・ R ・ 3.6 / (60 ・ Nt), where Nt: total gear ratio R; tire effective radius [m] Can be calculated. In addition, 3.6 is [m /
It is a coefficient for converting the vehicle speed calculated in the unit of [s] into the unit of [km / h].

At non-lockup, | VSP-VSPe
|> Β. Compared to the lockup when the torque converter input shaft and output shaft are directly connected in the non-lockup state, the effect on the engine rotation from the vehicle is smaller (rotational fluctuation is smaller). Not due to stability. The feedback control is prohibited during non-lockup in order to avoid erroneously determining that the rotation fluctuation has decreased due to the stable combustion even when the rotation fluctuation decreases due to the switching of the lockup mechanism from operation to non-operation.

<5> When all of the above items <1> to <4> are not satisfied, the elapsed time is equal to the predetermined value TML.
Within LC # (step 35 in FIG. 7). This is a delay process because the feedback control is not waited for (or restarted) immediately after the condition is met, but after waiting for the time TMLLC #, the feedback control is started. The delay processing is performed because Lljd as the stability signal is the filter processing output, so that the output is not stable immediately even if it is affected by disturbance, and the rotation fluctuation caused by gear change etc. Because it does not disappear instantaneously due to the influence of the vibration system, and the rotation fluctuation is not stable immediately after switching from non-lockup to lockup, it is better to perform delay processing for stable feedback control. Because it is good.

When the above conditions <1> to <5> are not satisfied, the feedback control inhibition flag is set to "0".
And enter feedback control (step 3 in FIG. 7).
7).

[3] Calculation of Stabilized Fuel-Air Ratio Correction Coefficient In FIG. 8, the stability signal (digital filter processing output Lljd) is sampled every 180 degrees and the number of samples is counted (step 4 in FIG. 8).
1).

The number of samples (value corresponding to the update cycle of the stabilized fuel-air ratio correction coefficient) L to be compared with this count value is obtained by referring to the table having the contents of FIG. 9 (step 4 in FIG. 8).
2).

It is determined that the update timing has come when the number of L samples is equal, the slice level SL is subtracted from the value obtained by dividing the total of sample data by L, and the table having the contents shown in FIG. The updated amount Dlldml is obtained by reference, and using this value, Lldml = Lldml _n-1 + Dlldml (6) where Lldml _n-1 ; the stabilized fuel-air ratio correction coefficient Lldml is calculated by the formula of Lldml one time before. Update (steps 43, 44, 45, 46 in FIG. 8).

The update amount Dlldml of the equation (6) is shown in FIG.
As shown in, the (sample data total / L-SL) is large in the positive region according to the (sample data total / L-SL), and the (sample data total / L-SL) is negative in the region. The value is increased by a negative value according to the total sample data / L-SL |.

Since the air-fuel ratio is changed by the stabilized fuel-air ratio correction coefficient Lldml, the update amount Dl is small even in the range where (total sample data / L-SL) is small in FIG.
When ldml is given, torque fluctuation occurs due to the change of the air-fuel ratio. In order to prevent this, in FIG. 10, when the value of the dead zone (total sample data / L-SL) is within a predetermined range centered on 0, a region where Dlldml = 0 is set)
Is provided.

Finally, the stabilized fuel-air ratio correction coefficient Lldml
When is less than the minimum value of 0, set Lldml = 0,
When Lldml becomes the maximum value LLDMMX # or more,
Let Lldml = LLDMMX #.

[4] Calculation of target fuel-air ratio First, the map value correction of the target fuel-air ratio and the calculation of the damper value Dml of the target fuel-air ratio are performed at every crank angle of 180 degrees as shown in FIG. Execute (steps 6 to 1 in FIG. 3)
1).

[4-1] Correction of map value of target fuel-air ratio Stabilized fuel-air ratio correction coefficient Lldml obtained as described above
Then, the map correction value Tdml of the target fuel-air ratio is calculated by the following equation: Tdml = Mdml × Lldml (7) where Mdml: map value of the target fuel-air ratio (step 6 in FIG. 3).

Since the map value (basic value of the target air-fuel ratio) Mdml of the target fuel-air ratio of the equation (7) is different between the lean condition and the non-lean condition, as shown in FIG. The MDMLL map (meaning lean map) having the contents is referred to, and when the lean condition is not satisfied, the MDMLS map (meaning non-lean map) having contents shown in FIG. 14 is referred to and referred to. The values are put in the variable Mdml (steps 82 and 83 and steps 82 and 84 in FIG. 12). 13,
In FIG. 14, the map value of 1.0 is equivalent to the theoretical air-fuel ratio,
If the value is smaller than this, the lean side air-fuel ratio is obtained, and conversely, if the value is larger than this, the rich side air-fuel ratio is obtained.

[4-2] Target Fuel-Air Ratio Damper Value Dml As shown in FIG. 15, the waveform of the damper value Dml shows the lamp response to the map correction value Tdml which changes stepwise when the air-fuel ratio is switched. It was done. Specifically,
, The air-fuel ratio change speed in the lean direction is Dmll,
If the air-fuel ratio change speed in the rich direction is Dmlr, it is possible to know in which direction the change is made by comparing the damper value Dml and the map correction value Tdml. Therefore, Dml <Td
If it is ml, it is assumed that the air-fuel ratio is switched to the rich direction, and the damper value Dml is Dml = Dml _n-1 + Dmlr However, Dml _n-1 ; updated by the formula of Dml one time before, and Dml exceeds Tdml. When D
By setting ml = Tdml (steps 7, 8 and 9 in FIG. 3), the damper value at the time of switching to the stoichiometric air-fuel ratio can be obtained. Further, when Dml ≧ Tdml, it is time to switch to the lean air-fuel ratio, so the damper value Dml is updated by the equation Dml = Dml−Dmll, and Dml <Tdml is set to Dml = Tdml (steps 7 and 10 in FIG. 3). , 11).

The reason why the damper process is performed at the time of switching the air-fuel ratio is to prevent a sudden change in the torque by the gentle switching of the air-fuel ratio and to make the operating performance appropriate.

[4-3] Target fuel-air ratio Tfbya This is calculated as follows: Tfbya = Dml + Ktw + Kas (8) where Ktw: water temperature increase correction coefficient Kas: post-start increase correction coefficient (step 71 in FIG. 11). .

The increase correction coefficient Kas after the start of the equation (8) is
During cranking, the value is determined according to the cooling water temperature, the value gradually decreases with time immediately after the engine is started, and the water temperature increase correction coefficient Ktw is a value obtained from the cooling water temperature by referring to a table, and both are known. From equation (8), the damper value Dml is 1.0 (that is, equivalent to the theoretical air-fuel ratio) during warm-up immediately after cold start, and the air-fuel ratio during warm-up is theoretically calculated by the warm-up increase (Kmr and Ktw). It shifts to the rich side of the air-fuel ratio.

It should be noted that the wide-range air-fuel ratio sensor 9 is sufficiently activated, that the time after start has passed to such an extent that there is no problem in drivability even if there is no increase in amount after start, and that the water temperature Tw has exceeded a predetermined value. When all of the above are satisfied, the air-fuel ratio sensor 9
Based on this, feedback control of the air-fuel ratio is started. Under this air-fuel ratio feedback control condition, Tfbya = 1.
It becomes 0, and the three-way catalyst 19 is utilized to the maximum extent.

When the lean condition is satisfied and the feedback control of the air-fuel ratio is performed based on the stability of combustion, the air-fuel ratio feedback correction coefficient α described later is 1.0.
And the stability control is performed by the stabilized fuel-air ratio correction coefficient Lldml via the target fuel-air ratio Tfbya.

[5] Calculation of fuel injection pulse width This is executed at a cycle of 10 ms as shown in FIG.

The fuel injection pulse width Ti output to each injector 4 is Ti = (Avtp + Kathos) × Tfbya × (α + αm) + Ts (9) where Avtp: cylinder air amount equivalent pulse width Kathos; wall flow correction amount α; empty The fuel ratio feedback correction coefficient αm; the air-fuel ratio learning correction coefficient Ts; the invalid pulse width is given by the equation (step 75 in FIG. 11).

Here, the cylinder air amount equivalent pulse width Avtp of the equation (9) is Avtp = Tp × Fload + Avtp _n−1 × (1−Fload) (10) where Tp; basic injection pulse width Avtp _n−1 The value of the basic injection pulse width Tp calculated from the formula of the previous Avtp Fload; weighted average coefficient (Fig. 11)
Step 74), and Tp is calculated from the intake air flow rate Qs obtained by A / D converting the air flow meter output and then linearizing it: Tp = (Qs / Ne) × K # × Ktrm (11) where K #; A constant Ktrm that determines the basic air-fuel ratio; a value that is calculated by the formula of a constant that is determined from the flow characteristics of the injector (steps 72 and 7 in FIG. 11).
3). The expressions (9), (10), and (11) are also known.

The wall flow correction amount Kathos of the equation (9) is intended to correct the low frequency component of the wall flow (the wall flow component that changes relatively slowly), and the equilibrium deposit amount Mf for each operating condition.
The value h is stored, and the change in the equilibrium adhesion amount due to the transient is added as a total correction amount to the cylinder air amount equivalent pulse width Avtp (subtracted during deceleration) at a predetermined ratio for each fuel injection. It is known. For example, when accelerating, the injection amount must be increased, but no matter how good the atomization characteristics of the injector, a part of the fuel adheres to the intake manifold wall and flows in the liquid state along the intake pipe wall. Flow is wall flow), flowing into the cylinder at a slower rate than the fuel entrained in the air. That is, since the air-fuel mixture drawn into the cylinder is temporarily thinned by the wall-flow fuel, the wall-flow correction amount Kathos is increased at the time of acceleration in order to prevent the temporary lean mixture. On the contrary, during deceleration when the manifold pressure suddenly becomes a high negative pressure, the fuel adhering to the manifold wall is vaporized all at once,
The air-fuel mixture becomes temporarily too rich, and CO and HC increase. Therefore, during deceleration, the vaporized wall flow is reduced.

Note that when a constant fuel cut condition, such as during deceleration or high rotation, is reached, the invalid pulse width Ts is stored in place of Ti in equation (9) (otherwise, Ti is stored in the output register (see FIG. By performing Steps 77 and 79 and Steps 77 and 78 of 11), preparation for injection at the injection timing is performed.

Here, the operation of this example will be described when the lean condition is satisfied (at this time, the air-fuel ratio feedback control based on the air-fuel ratio sensor 9 is not performed).

Under the lean condition, the feedback correction amount (stabilized fuel-air ratio correction coefficient Lldml) is updated so that the stability signal coincides with the slice level SL which is the target stability value, and the target fuel amount is adjusted with this feedback correction amount. The map value (Mdml) of the sky ratio is corrected. For example, when the combustion stability deteriorates, the digital filter processing output Lljd, which is the stability signal, increases, so the stabilized fuel-air ratio correction coefficient Lldml is updated to the larger side, and the target is calculated by the above equation (7). The map correction value Tdml of the fuel-air ratio also becomes large. Since the air-fuel ratio is shifted to the rich side, the stability of combustion is improved, and the digital filter processing output Lljd is shifted to the smaller side this time. As the stability feedback control is repeated, the stability signal eventually settles at the stability target value.

On the other hand, in the non-lockup state, the digital filter processing output Llj which is a stability signal as compared with the lockup state in which the input shaft and the output shaft of the torque converter are directly connected
Since d becomes small, in this case as well, if the stability of the vehicle is improved and the stabilized fuel-air ratio correction coefficient Lldml is updated to a smaller side, the air-fuel ratio is erroneously controlled to the lean side. . When the vehicle is not locked up, the stability signal of the vehicle does not improve just because the stability signal becomes smaller in response to the smaller influence of the vehicle on engine speed fluctuations than when the vehicle is locked up. is there.

On the other hand, in this example, when the absolute value | VSP-VSPe | of the difference between the actual vehicle speed and the predicted vehicle speed exceeds the predetermined value β, it is determined that the vehicle is not locked up. Since the stability fuel-air ratio correction coefficient Lldml is prohibited from being updated (that is, the feedback control based on the stability signal is prohibited), the stability fuel-air ratio correction coefficient Lldml erroneously leans the air-fuel ratio during non-lockup. It is never updated on the side of

Further, in the M / T vehicle, when the engine rotation is stabilized by idling, the digital filter processing output Lljd, which is the stability signal, becomes smaller than when the clutch is engaged. Therefore, also in this case, the vehicle stability is good. However, if the stabilized fuel-air ratio correction coefficient Lldml is updated to the decreasing side (direction to make the air-fuel ratio leaner), erroneous control will occur.
It is determined that there is a possibility that idling is being performed due to | VSP-VSPe |> β, and feedback control based on the stability signal is prohibited, so that the engine and the vehicle drive system are not in a direct connection state. It is possible to prevent erroneous control that occurs as a result.

In the lock-up mechanism, the lock-up piston in the torque converter is engaged and released by the lock-up signal (ON / OFF signal to the lock-up solenoid). You can also determine if it is time. However, if the amount of slippage of the clutch increases over time, it will be in the same state as when not locked up (that is, the engine and the drive system of the vehicle will be in a direct connection state), but if it is based on the lockup signal, Also misunderstands that it is a lockup. On the other hand |
When determining whether or not the vehicle is in the non-lockup state by comparing VSP-VSPe | and β, it is determined that the vehicle is in the non-direct coupling state even when a large slip occurs in the clutch, and the non-direct coupling state is determined. The accuracy of the judgment as to whether or not is improved.

In the case of an M / T vehicle, if a switch that is turned on when the clutch is disengaged is provided, it is possible to determine whether or not the clutch is disengaged (even when the clutch is half-clutched) by the signal from this clutch switch. You can also

FIG. 16 shows NOx which is a harmful component in exhaust gas.
Is a so-called EGR device that recirculates an inert exhaust gas to the intake pipe in order to suppress the generation of the EGR passage 103, which connects the intake pipe 101 and the exhaust pipe 102,
EGR valve 1 for adjusting the gas flow rate in this passage 103
04, a negative pressure control valve 105 for adjusting the control negative pressure to the EGR valve 104.

The negative pressure control valve 105 introduces the negative pressure of the intake pipe downstream of the intake throttle valve through the passage 105c to generate a constant negative pressure, and the atmospheric pressure is introduced into the constant negative pressure. And a solenoid valve 105b that creates a control negative pressure to the EGR valve 104 by
The GR valve flow rate is determined almost in proportion to the OFF duty to the solenoid valve 105b (the valve closing time ratio of the constant cycle) (the larger the OFF duty, the larger the EGR flow rate).
Is used as the control value for the.

In this EGR device, the EGR is performed under the EGR condition.
The maximum temperature during combustion is lowered by opening a valve and mixing a certain amount of exhaust gas (EGR gas) into the intake air. The target value of the EGR rate (ratio between EGR gas amount and fresh air amount) is the engine. Therefore, the control unit 2 controls the OFF duty to the solenoid valve 105b so that the target EGR rate according to the operating condition is obtained.

In this case, if the actual EGR rate deviates from the target value or the environmental conditions (for example, intake air temperature and humidity) change with the aging of the EGR valve 104, the solenoid valve 105b, etc., the combustion is stabilized. Degree changes,
Stability control can be performed by feedback-controlling the EGR rate. In the control unit 2,
When the EGR condition is reached, the EG is adjusted so that the combustion stability signal detected from the rotation fluctuation falls below the slice level SL.
By updating the R rate correction amount and correcting the basic value (map value) of the target EGR rate with this correction amount, EGR can be performed efficiently while stabilizing combustion.

However, also in this example, if it is not taken into consideration that the fluctuation in rotation due to the fact that the engine and the vehicle drive system are not in the direct connection state during non-lockup is taken into consideration, the operation is performed immediately after returning to the direct connection state. Sex may deteriorate. Further, the EGR rate is erroneously controlled to a smaller side, the combustion temperature cannot be lowered sufficiently, and NOx increases.

Therefore, also in this example, when the absolute value of the difference between the actual vehicle speed VSP and the predicted vehicle speed VSPe exceeds the predetermined value β, it is determined that there is no lockup, and feedback control based on the stability signal is performed. By prohibiting (steps 124 and 126 in FIG. 18), the same effect as that of the previous embodiment can be obtained.

17 to 23 show the control routine of this example and the characteristic diagrams showing the contents of the tables and maps used in this routine, the stability control method is the same as that of the previous embodiment.

By associating these with the previous embodiment, FIG. 17 is FIG. 3, FIG. 18 is FIG. 7, and FIG. 19 is FIG.
20 corresponds to FIG. 10, FIG. 21 corresponds to FIG. 11, FIG. 22 corresponds to FIG. 12, and FIG. 23 corresponds to FIG.
The routine of FIG. 3 and the characteristic diagrams of FIGS. 5, 6 and 9 are also shared in this example.

However, in the case of the fuel-air ratio, the larger the value, the more stable the combustion becomes, whereas in the case of the EGR rate, the opposite of the fuel-air ratio (the larger the EGR rate, the more unstable the combustion becomes. ), The updated amount Dll of the stabilized EGR rate correction coefficient
The EGR characteristic (FIG. 20) is opposite to the characteristic of the updated amount Dlldml of the stabilized fuel-air ratio correction coefficient (FIG. 10). Although the map of FIG. 23 is shown by the EGR rate [%],
The R valve opening may be used.

[0093]

According to the first aspect of the present invention, the stability of the engine is detected from the fluctuation of the engine rotation, the value on the lean side of the theoretical air-fuel ratio is set as the target air-fuel ratio under the lean condition, and the stability is detected. While the feedback control of the air-fuel ratio is performed so that the value matches the predetermined stability target value, the air-fuel ratio feedback control is prohibited when the engine and the vehicle drive system are in a non-direct connection state. Incorrect control of the fuel ratio to the lean side can be avoided, and even if there is a reduction in rotation fluctuation due to the engine and the vehicle drive system not being directly connected, the drivability immediately after returning to the direct connection state will deteriorate. There is no.

In a second aspect based on the first aspect, the feedback control means comprises means for calculating a target air-fuel ratio on the lean side of the stoichiometric air-fuel ratio under lean conditions, and the stability detection value having a predetermined stability. Temperature correction target value, a means for calculating an air-fuel ratio correction amount, a means for correcting the target air-fuel ratio under the lean condition with this air-fuel ratio correction amount, and a fuel injection based on the corrected target air-fuel ratio. Since it is composed of a means for calculating the amount and means for supplying this fuel injection amount to the intake pipe, in addition to the effect of the first aspect of the invention, a conventional configuration for feedback controlling the air-fuel ratio with the theoretical air-fuel ratio as the target, and The value of the map used for this control can be used as it is, and the man-hour for creating the map can be reduced.

A third aspect of the present invention detects the stability of the engine from fluctuations in the engine rotation, sets a value corresponding to the operating condition signal under the EGR condition as the target EGR rate, and the detected value of the stability is a predetermined stability. The feedback control of the EGR rate is performed so as to match the engine target value, while the feedback control of the EGR rate is prohibited when the engine and the vehicle drive system are not directly connected to each other. Even if there is a decrease in rotational fluctuation due to not being directly connected, the drivability immediately after returning to the direct connection state is not deteriorated, and the EGR rate is not erroneously controlled, so an increase in NOx is prevented. be able to.

In a fourth aspect based on the third aspect, the feedback control means comprises means for calculating a target EGR rate according to an operating condition signal under an EGR condition, and the stability detection value is a predetermined stability level. A means for calculating the EGR rate correction amount so as to match the target value, and the EGR rate correction amount
In addition to the effect of the third aspect of the invention, it is composed of means for correcting the target EGR rate under the GR condition and means for controlling the opening degree of the flow control valve in the EGR passage based on the corrected target EGR rate. Thus, the conventional configuration for controlling the EGR rate to be open and the value of the map used for this control can be used as they are.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the non-coupling state determination means detects a sensor for detecting an engine speed and a gear position of a transmission. A sensor, a means for calculating a vehicle speed predicted value from the detected values of the gear position and the engine speed, a sensor for detecting an actual vehicle speed, and comparing the actual vehicle speed with the vehicle speed predicted value, the absolute difference between the two is detected. When the value exceeds a predetermined value, it is configured to be in a non-direct connection state. Therefore, in addition to the effect of any one of the first to fourth inventions, the A / T
Large slippage of the clutch due to deterioration over time, compared to the case of determining the non-direct connection state in the vehicle from the lockup signal or the case of determining the non-direct connection state in the M / T vehicle from the depression amount of the clutch pedal, etc. Also, it can be determined that the non-direct connection state is established, and the accuracy of the determination as to whether or not the non-direct connection state is improved.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the first invention.

FIG. 2 is a control system diagram of a lean burn engine according to an embodiment.

FIG. 3 is a flow chart of a 180 degree job.

FIG. 4 is a flowchart for explaining calculation of rotation fluctuation.

FIG. 5 is a waveform diagram showing the relationship between combustion pressure, rotation speed, and reference signal in the case of a 4-cylinder engine.

FIG. 6 is a waveform diagram for explaining a measurement section.

FIG. 7 is a flowchart for explaining determination of feedback control conditions.

FIG. 8 is a flowchart for explaining calculation of a stabilized fuel-air ratio correction coefficient Lldml.

FIG. 9 is a characteristic diagram showing the contents of a table of a predetermined sample number L.

FIG. 10: Update amount D of stabilized fuel-air ratio correction coefficient Lldml
It is a characteristic view which shows the table content of lldml.

FIG. 11 is a flowchart of a 10 msec job.

FIG. 12 is a flowchart of a background job.

FIG. 13 is a characteristic diagram showing the contents of a lean map.

FIG. 14 is a characteristic diagram showing the contents of a non-lean map.

FIG. 15 is a waveform diagram when switching the air-fuel ratio.

FIG. 16 is a control system diagram of an EGR control device of another embodiment.

FIG. 17 is a flowchart of a 180-degree job.

FIG. 18 is a flowchart for explaining determination of feedback control conditions.

FIG. 19 is a flowchart for explaining calculation of a stabilized EGR rate correction coefficient L1EGR.

FIG. 20 is a characteristic diagram showing the table contents of the updated amount DllEGR of the stabilized EGR rate correction coefficient LlEGR.

FIG. 21 is a flowchart of a 10 msec job.

FIG. 22 is a flowchart of a background job.

FIG. 23 is a characteristic diagram showing the content of a map value MEGR of a target EGR rate.

FIG. 24 is a diagram corresponding to claims of the second invention.

FIG. 25 is a diagram corresponding to the claim of the third invention.

FIG. 26 is a diagram corresponding to the claim of the fourth invention.

FIG. 27 is a diagram corresponding to the claim of the fifth invention.

[Explanation of symbols]

 2 control unit 3 fuel injection valve (fuel supply means) 4 air flow meter 6 throttle sensor 7 crank angle sensor 9 wide range air-fuel ratio sensor 19 three-way catalyst 31 engine stability detection means 32 lean condition determination means 33 air-fuel ratio feedback control means 34 non Direct connection state determination means 35 Feedback control prohibition means 41 Target air-fuel ratio calculation means 42 Air-fuel ratio correction amount calculation means 43 Target air-fuel ratio correction means 44 Fuel injection amount calculation means 45 Fuel supply means 51 EGR condition determination means 52 EGR rate feedback control means 53 Feedback control prohibition means 61 Target EGR rate calculation means 62 EGR rate correction amount calculation means 63 Target EGR rate correction means 64 EGR valve opening control means 71 Engine speed sensor 72 Gear position sensor 73 Vehicle speed predicted value calculation means 74 Vehicle speed set Sensor 75 Non-direct connection state determination means 103 EGR passage 104 EGR valve 105b Solenoid valve

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area F02M 25/07 550 R

Claims (5)

[Claims] 1. A means for detecting the stability of an engine from fluctuations in the engine rotation, a means for judging whether or not an operating condition signal is a lean condition, and a result of this judgment that is leaner than the stoichiometric air-fuel ratio on the lean side. Whether the value is set as the target air-fuel ratio and the means for performing feedback control of the air-fuel ratio so that the detected value of the stability matches the predetermined stability target value and the engine and the vehicle drive system are not directly connected An engine stability control device comprising means for determining whether or not the result of this determination and means for inhibiting feedback control of the air-fuel ratio in a non-direct connection state. 2. The feedback control means includes means for calculating a target air-fuel ratio leaner than the stoichiometric air-fuel ratio under lean conditions, and an air-fuel ratio so that the detected stability value matches a predetermined stability target value. A means for calculating the correction amount, a means for correcting the target air-fuel ratio under the lean condition with this air-fuel ratio correction amount, a means for calculating the fuel injection amount based on the corrected target air-fuel ratio, and this fuel injection The engine stability control device according to claim 1, further comprising: a means for supplying a quantity to the intake pipe. 3. A means for detecting engine stability from engine speed fluctuations, a means for judging whether or not an operating condition signal is an EGR condition, and a value corresponding to the operating condition signal under the EGR condition from the result of this judgment. Is a target EGR rate, and whether the means for performing feedback control of the EGR rate so that the detected value of the stability matches a predetermined stability target value and the engine and the drive system of the vehicle are not directly connected to each other. An engine stability control device comprising means for determining whether or not the result of this determination and means for inhibiting feedback control of the EGR rate in a non-direct connection state. 4. The feedback control means comprises means for calculating a target EGR rate according to an operating condition signal under an EGR condition, and an EGR rate correction so that the detected stability value matches a predetermined stability target value. A means for calculating the amount and this EGR
A means for correcting the target EGR rate under the EGR condition with a rate correction amount, and an EG based on the corrected target EGR rate.
4. The engine stability control device according to claim 3, further comprising means for controlling the opening of the flow control valve in the R passage. 5. A vehicle speed prediction value is calculated from the sensor for detecting the engine speed, a sensor for detecting the gear position of the transmission, and the detected values of the gear position and the engine speed. Means, a sensor for detecting the actual vehicle speed, and means for comparing the actual vehicle speed with the vehicle speed predicted value and determining the non-direct connection state when the absolute value of the difference between the two exceeds a predetermined value. 5. The engine stability control device according to claim 1, wherein the stability control device is configured.