JP2906052B2 - Engine exhaust recirculation control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas recirculation control device for an engine that changes an air-fuel ratio in a specific operation region. (Prior Art) Conventionally, in a steady region, an engine is usually operated near a stoichiometric air-fuel ratio. In particular, CO in the exhaust gas by the three-way catalyst, the engine so as to reduce the HC and NOx, have feedback control of the air-fuel ratio in the steady state based on the output of the O ₂ sensor in the vicinity of the stoichiometric air-fuel ratio of 14.7 Was. And, even in an engine operating at the stoichiometric air-fuel ratio, the air-fuel ratio often shifts to a side thinner than the stoichiometric air-fuel ratio. The exhaust gas recirculation amount (EGR amount) is increased in order to cope with a decrease in the NOx purification rate by the three-way catalyst when the shift to the thin side occurs. In addition, the engine must be operated near the stoichiometric air-fuel ratio as described above in terms of output and emission, or in some cases with a richer mixture than that, but in terms of fuel efficiency, it is required to operate as lean as possible without misfiring. It is well known that is more advantageous. Therefore,
In order to improve the fuel efficiency of the engine, it has been considered to perform a lean burn operation by switching to a lean air-fuel mixture in a specific operation region where high output is not required. By the way, when the air-fuel ratio is switched to the lean side in the specific operation range as described above, the three-way catalyst is also used.
Actively lean on the E side to address the decline in NOx purification rates
GR needs to be done. However, when the EGR is performed in this manner on the lean side, or particularly when the EGR amount is relatively increased on the lean side, the
When performing transient correction of R, there is a problem that combustion becomes unstable and running performance deteriorates.It is clear that this is due to sudden EGR fluctuation during transient correction and response delay of EGR device. Was. That is, in general, in order to compensate for the delay in the operation response of the EGR valve, acceleration correction for increasing the EGR during acceleration is performed, while deceleration correction for decreasing the EGR during deceleration is generally performed. However, when the air-fuel ratio is lean, the EGR limit is low, so that the combustion tends to deteriorate due to the EGR fluctuation. In particular, when the EGR amount is increased on the lean side, the margin to the EGR limit is small, so if the normal EGR acceleration correction is performed during acceleration, the EGR amount will be excessive, and misfiring is likely to occur . Further, if the normal deceleration correction is performed at the time of deceleration, the weight loss becomes insufficient, the EGR amount temporarily becomes excessive, and a misfire also occurs. (Object of the Invention) The present invention has been made to solve the above problem in lean operation with a low EGR limit, and has been made in order to solve the above problem. The purpose of the present invention is to prevent instability. (Structure of the Invention) The present invention solves the above-mentioned problem by changing the transient correction amount of EGR in accordance with the air-fuel ratio of the engine. The structure is as follows. That is, the engine exhaust gas recirculation control device according to the present invention
As shown in the figure, while operating at a predetermined air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, air-fuel ratio is set to perform lean-burn operation by switching to an air-fuel ratio leaner than the predetermined air-fuel ratio in a specific operation region. An exhaust gas recirculation control device for an engine, comprising: a fuel ratio setting unit; and an air-fuel ratio adjusting unit that adjusts an air-fuel ratio of the engine so as to have an air-fuel ratio set by the air-fuel ratio setting unit. Exhaust gas recirculation amount setting means for setting a basic control amount of the exhaust gas recirculation amount to the intake system of the engine; exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount to the intake system so as to become the set exhaust gas recirculation amount;
Transient determination means for determining engine transient time; transient correction means for setting a correction amount for correcting the basic control amount at the time of engine transition determined by the transient determination means to correct the exhaust gas recirculation amount to the intake system; The correction amount by the transient correction means is increased according to the air-fuel ratio set by the air-fuel ratio setting means when performing the lean burn operation as compared with when operating at a predetermined air-fuel ratio near the stoichiometric air-fuel ratio. And a transient correction amount correction means for correcting the correction value to be smaller on the side. (Operation) In a steady state, the amount of exhaust gas recirculation is set according to the operating state of the engine, and the amount of exhaust gas recirculation to the intake system is adjusted so as to achieve the set amount of exhaust gas recirculation. In addition, during transients such as acceleration and deceleration, the exhaust gas recirculation amount is corrected, and when the lean amount combustion operation is performed in accordance with the set value of the air-fuel ratio, the operation is performed at a predetermined air-fuel ratio near the stoichiometric air-fuel ratio. It is corrected so that it becomes smaller on the increasing side than that. (Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 2 shows an embodiment of the present invention. The engine 1 according to this embodiment includes an injector 3 for fuel injection in an intake passage 2 and a three-way catalyst 5 in an exhaust passage 4. The fuel from the fuel tank 6 is pressurized by the fuel pump 8 on the way through the fuel supply passage 7 to the injector 3, passed through the fuel filter 9, and sent to the injector 3. The fuel supply passage downstream of the fuel filter 9 and the fuel tank 6 are connected by a return passage 10, and a fuel pressure regulator 11 is provided in the return passage 10. In addition, a surge tank 12 is formed in an intake passage upstream of the injector 3, and further upstream thereof is open to an air cleaner 13. A throttle valve 15 driven by an electric throttle actuator 14 is provided immediately downstream of the surge tank 12. Also, a throttle valve upstream of the three-way catalyst 5 in the exhaust passage 4 and a throttle valve in the intake passage 2
The downstream portion 15 is communicated with a communication passage (EGR passage) 16 for exhaust gas recirculation (EGR). The EGR passage 16 is provided with a negative pressure operated EGR valve 17. Negative pressure chamber of EGR valve 17
18 is connected to the intake passage 2 downstream of the throttle valve 15 by a negative pressure intake passage 19, and in the middle of the negative pressure intake passage 19,
A negative pressure solenoid 20 for adjusting the intake amount of the intake pipe negative pressure into the negative pressure chamber 18 and the leak amount to the atmosphere is provided. The control unit 21 controls the injector 3, the throttle actuator 14 for driving the throttle valve 15, and the negative pressure solenoid 20 for adjusting the opening amount of the EGR valve 17. The control unit 21 receives an engine speed signal from the distributor 22, an intake air amount signal from an air flow sensor 23 provided downstream of the air cleaner 13, and an O ₂ sensor 24 provided in the exhaust passage 4 upstream of the three-way catalyst 5. Accelerator position sensor that detects the air-fuel ratio signal of the vehicle and the amount of depression of the accelerator 25
Water temperature sensor that detects the output of 26 and the temperature of engine cooling water
27, the output of an intake air temperature sensor 28 provided immediately downstream of the air cleaner 13, the output of a throttle position sensor 29 that detects the opening of the throttle valve 15, and the like. The control unit 21 is connected to the battery 30 and outputs signals for fuel injection control, throttle valve control and EGR valve control, and also outputs an ignition signal to the igniter 31. The control of the air-fuel ratio in this embodiment is performed as follows. First, a fuel injection amount according to the engine speed and the intake air amount is calculated, and a basic injection amount is determined in a form obtained by adding a correction based on the water temperature and the intake air temperature. Then, whether the region performing lean burn judged by change of the opening degree of the throttle valve 15, that it when the throttle opening change is large are usually controlled area when, if the feedback area of the O ₂ sensor output Feedback control of the air-fuel ratio based on the Specifically, the fuel injection amount is determined by multiplying the basic injection amount by the feedback coefficient, and the injector 3 is driven by the injection pulse having a pulse width corresponding to the fuel injection amount, and the air-fuel ratio is set to a value close to the stoichiometric air-fuel ratio. Is controlled to a predetermined range. The feedback coefficient is obtained from the output ratio _KFB of the O ₂ sensor based on the target air-fuel ratio shown in FIG. In the steady state where the throttle opening change is not so large, lean correction is performed in accordance with the target air-fuel ratio set to a lean value, and an injection pulse with a pulse width obtained by adding acceleration correction according to the throttle opening change is output. And inject fuel. In such a lean burn region, the opening degree of the throttle valve 15 is corrected to increase as the air-fuel ratio increases. The opening of the throttle valve 15 is basically the accelerator 25
Is determined in accordance with the amount of depression. The basic throttle opening is as shown in FIG. 3 (e). Figure 3 (a) to the correction by the control gain as shown in TG ₁ is added thereto. However, when the air-fuel ratio control is switched to the control on the lean side, the above-described correction of the throttle opening is not immediately performed, but is started after a predetermined period. The throttle opening finally determined is a value obtained by adding the above correction and the EGR correction described later to the basic opening as described later. When it is not in the EGR region, the EGR correction is of course zero. The control of the EGR is performed by controlling the negative pressure in the negative pressure chamber 18 of the EGR valve 17 with the negative pressure solenoid 20. That is, the EGR region is determined according to the operating state of the engine, and E
In the GR region, the lift amount of the EGR valve is controlled by adjusting the operating negative pressure so as to obtain an EGR amount suitable for each operation state. The lift amount of the EGR valve is feedback-controlled to a target value based on the output of the EGR valve position sensor 32. In addition, in order to cope with a decrease in the NOx purification rate by the three-way catalyst in the lean burn region, in such a region where the air-fuel ratio is large, the EGR amount is increased to increase the NOx reduction effect by the EGR. . The EGR increase area is an area indicated by oblique lines in FIG. 3 (c). However, when switching from the stoichiometric air-fuel ratio range to the lean burn range, the air-fuel ratio does not immediately become lean due to a response delay of the fuel control, so that the increase in the EGR for a predetermined period is delayed. The EGR performs an increase correction during acceleration and performs a decrease correction during deceleration. However, in the region where the air-fuel ratio is lean, in order to prevent deterioration of combustion due to EGR fluctuation, as shown in FIG. During deceleration, the leaner the EGR, the greater the deceleration correction amount of the EGR, and the faster the reduction. During acceleration, the leaner, the smaller the acceleration correction amount, and the later the increase. The throttle opening is further increased to compensate for a decrease in output during lean burn due to such EGR. Therefore, the final throttle opening in the lean burn region is obtained by changing the basic throttle opening corresponding to the accelerator opening as shown in FIG. 3 (e) to a leaning as shown in FIG. 3 (a). Control gain TG ₁ to deal with and control gain TG to deal with EGR
_It is corrected by ₂ . FIGS. 4 and 5 are flowcharts for executing the above control. FIG. 4 shows a subroutine for determining a correction value of the throttle opening. This is the main routine of control. In the figure, S _{1 to} S ₄₂ and M _{1 to} M ₅ indicate each step. In FIG. 4, the process is started (S ₁ ), and a flag of λ = 1 is set (S ₂ ). Then, the engine rotational speed S ₃ Ne, intake air quantity Q _A, enter the throttle opening TVO and the cooling water temperature T _W, determine the Q as the throttle opening change ΔTVO in S _4. Then, to determine the basic injection quantity Ti as a function of Q _A and Ne at S _5. Then cooling water temperature T _W of the engine in S _6, it is determined whether or not higher than the predetermined value T _WS, but do nothing unless higher, turn if that becomes high throttle opening at S ₇ Lean shift determination is made based on whether the degree change Q is smaller than a predetermined value _QLN . Then, Q is go to S ₈ when not smaller than Q _LN, the basic injection amount T _i to the feedback coefficient K excess air factor in a form multiplied by _FB lambda = 1 the pulse width T _FI
Determines, (S ₉₎ as a lean coefficient K _LN, in S ₁₀ T _FI
Stored as a learning value go to S _14. Further, if there is YES, that lean shift determination in S _7, S ₁₁
To attract lean coefficient K _LN from the map based on the engine speed intake air quantity by performing, after turning on the lean flag in S _12, to determine the pulse width T _FLI determine the lean target air-fuel ratio in S _13. T _FLI is obtained by calling the pulse width T _FI of λ = 1, multiplying it by the lean coefficient K _LN , and further multiplying it by the correction coefficient K ′ at the time of lean acceleration. In S ₁₄ to determine the dolphins the lean flag is set. A feedback control region of the NO, i.e. lambda = 1 in S _7, if that does not stand the lean flag further performed S _14, whether the water temperature T _W go to S ₁₅ is larger than the predetermined value T _WS determine whether, when that T _W is not greater than T _WS is the process directly proceeds, T _W when is larger than T _WS is S ₁₆ with O ₂ input to lambda = 1 control S ₁₇ the output of the sensor It calculates the feedback coefficient K _FB, flags 2 in S _18. If that lean flag S ₁₄ is set, attract throttle control gain TG ₁ in accordance with the degree of lean go to S _19, thereby decided stores the throttle valve correction value at S _20. Then to determine whether to go to S ₂₁ flag 2 is set, the flag 2 is proceeded as if standing, if that flag 2 is set, which is the lean side from the lambda = 1 At the time of transition to control, S
Sets the timer T to zero go to _22, the timer T at S ₂₄ is counted up in S ₂₃ proceeds to the first time is larger than a predetermined value T ₂ above. That is, when the lean transition in relaxed speed state temporarily hold the correction value determined in S _20, to start the throttle correction control after a predetermined time. Then do cormorant judgment of whether the EGR in the S ₂₅ region.
Although not nothing if not EGR region, if that EGR region, attract throttle control gain TG ₂ for throttle correction during EGR go to S _26. Next, look at whether or not the lean flag is set at S _27, went to S ₂₈ if not standing, fundamental from the EGR map at the time of λ = 1 operation
Attract EGR amount M _ER, the flag 3 in S _29. Also, S
_{If the} lean flag is set at ₂₇ , S
To go to _30, attracting a large basic EGR amount M _EL than that at the time of λ = 1 operation from the EGR map. Then, to determine stores throttle valve correction value by performing the S _31. Next, it is determined whether the flag 3 in S ₃₂ stands. When the flag 3 is not set, the process proceeds as it is. Also, if that flag 3 has been set, also it determines whether or not the lean flag go to S ₃₃ is standing. Then, and flagged 3 in S _32, although it proceeds when no standing lean flag S _33, if that lean flag is set, the transition to lean from the operation thereof lambda = 1 Judging that it is time, then
It sets the timer T to zero at S _34, and counts up at S _35. Then, to see if the timer T at S ₃₆ exceeds a predetermined value T _1, the flag 3 is cleared if YES (S _37),
Go to S _38. Predetermined value Q of the throttle opening change the throttle opening change Q in S ₃₈ is whether the reference performing acceleration and deceleration correction of EGR
Determine if the _EGR is exceeded. And Q is Q
If that exceeds the _EGR attract EGR correction coefficient K _EGR during acceleration or deceleration to go to S _39. In addition,
The K _EGR at this time differs depending on the air-fuel ratio (lean coefficient K _LN ), and the leaner the K _EGR during acceleration, the larger the lean _EGR during deceleration. Then, to determine the EGR position as a target is multiplied by K _EGR basic EGR amount determined in S ₂₈ or S ₃₀ in S ₄₀ (M _ER or M _EL), to drive the EGR valve on the basis thereof (S ₄₁ ). Then, the lean flag and the flag 2 are lowered, and the process returns to the original state. Next, the throttle valve driving routine shown in FIG. 5 will be described. Starting at M _1, it reads the accelerator opening at M _2, to calculate a basic opening of the throttle valve from an accelerator opening at M _3. Then, go to M _4, fourth by adding the correction by the control gain TG ₁ and TG ₂ determined in the subroutine of Figure determines the final throttle opening degree, to drive the throttle valve 1 in M _5. In the above embodiment has been described applied to a fuel injection engine for feedback controlling the air-fuel ratio by an output of the O ₂ sensor, but the present invention is also for various engines with other air-fuel ratio control method applied can do. Further, the EGR device is not limited to the device controlled by the negative pressure solenoid as in the above-described embodiment, and various other types can be used. (Effect of the Invention) Since the present invention is configured as described above, it is possible to prevent misfiring from occurring due to excessive EGR during lean operation with a low EGR limit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall configuration diagram of the present invention, FIG. 2 is an overall view of one embodiment of the present invention, and FIGS. 3 (a) to 3 (e) explain control of the embodiment. FIG. 4 and FIG. 5 are flowcharts for executing the control of the embodiment. 1: Engine, 3: Injector, 17: EGR valve, 20: Negative pressure solenoid, 21: Control unit.

Claims (1)

(57) [Claims] Air-fuel ratio setting means for operating at a predetermined air-fuel ratio near the stoichiometric air-fuel ratio, and setting the air-fuel ratio to perform a lean burn operation by switching to an air-fuel ratio leaner than the predetermined air-fuel ratio in a specific operation region; An exhaust gas recirculation control device for an engine, comprising an air-fuel ratio adjusting means for adjusting an air-fuel ratio of an engine to be an air-fuel ratio set by an air-fuel ratio setting means, wherein an exhaust gas recirculation control device is provided to an intake system of the engine according to an operating state of the engine. Exhaust gas recirculation amount setting means for setting a basic control amount of the exhaust gas recirculation amount; exhaust gas recirculation amount adjusting means for adjusting the exhaust gas recirculation amount to the intake system so as to achieve the set exhaust gas recirculation amount; Transient determination means; transient correction means for setting a correction amount for correcting the basic control amount at the time of engine transition determined by the transient determination means to correct the exhaust gas recirculation amount to the intake system; According to the air-fuel ratio set by the air-fuel ratio setting means, the correction amount by the correction means, when performing the lean burn operation, on the increase side than when operating at a predetermined air-fuel ratio near the stoichiometric air-fuel ratio An exhaust gas recirculation control device for an engine, comprising: a transient correction amount correcting means for correcting the amount to be reduced. 2. 2. The exhaust gas recirculation control device for an engine according to claim 1, wherein the basic control amount is set to a larger value during the lean burn operation than when operating at a predetermined air-fuel ratio near the stoichiometric air-fuel ratio. 3. When the acceleration is determined by the transient determination means, the correction amount is set to correct the exhaust gas recirculation amount to the increasing side, and the correction amount to the increasing side is set by the air-fuel ratio set by the air-fuel ratio setting means. 2. The exhaust gas recirculation control device for an engine according to claim 1, wherein the smaller the value is, the smaller the value is. 4. When the deceleration is determined by the transient determination means, the correction amount is set to correct the exhaust gas recirculation amount to the reduction side, and the correction amount to the reduction side is set by the air-fuel ratio set by the air-fuel ratio setting means. 2. The exhaust gas recirculation control device for an engine according to claim 1, wherein the larger the value is, the greater the leanness is.