JP2522348B2 - Exhaust gas recirculation control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas recirculation (EGR) device that recirculates a part of exhaust gas to an intake system and re-combusts it.

[Conventional technology and problems]

Conventionally, in a multi-cylinder internal combustion engine equipped with an EGR device, a configuration is known in which the EGR rate is controlled so that the deviation between the combustion pressure in each cylinder and its average value (that is, engine roughness) becomes a predetermined value or less ( JP-A-59-46357). However, in this conventional device, since it is necessary to provide a combustion pressure sensor for each cylinder, the entire device is expensive, and the control becomes complicated, so that the calculation speed is relatively delayed as the engine speed increases, It has a problem of poor controllability.

An object of the present invention is to provide an exhaust gas recirculation control device that is easy to control and can reliably obtain a predetermined EGR rate regardless of the engine speed.

[Means for solving the problem]

As shown in the configuration diagram of the invention of FIG. 1, the present invention includes a recirculation control valve 37 provided in an exhaust gas recirculation passage connecting an intake system and an exhaust system, a combustion pressure sensor 37 provided in one cylinder, Means A for detecting the output torque difference of each cylinder, means B for adjusting the output torque of each cylinder so that the output torque difference is substantially eliminated, and after the output torque is adjusted, A means C for controlling the opening degree of the recirculation control valve according to the magnitude of the fluctuation of the combustion pressure is provided.

〔Example〕

 The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows a 4-cylinder engine to which an embodiment of the present invention is applied. Four ignition plugs 21, 22, 23, and 24 are attached to the engine body 11 corresponding to the first to fourth cylinders, and the intake manifold 12 and the exhaust manifold 13 are connected. Each branch pipe of the intake manifold 12 is provided with a fuel injection valve 31, 32, 33, 34. That is, these fuel injection valves are provided for each cylinder and are controlled independently of each other. A combustion pressure sensor 35 is provided in the first cylinder.

A throttle valve 15 is provided in the intake passage 14 connected to the upstream side of the intake manifold 12, and a throttle sensor 16 is connected to the valve shaft of the throttle valve 15. The throttle sensor 16 outputs an ON signal when the throttle valve 15 is substantially fully closed. Throttle valve 15 in intake passage 14
An air flow meter 36 is provided on the upstream side, and an air cleaner 17 is provided on the upstream side.

Intake manifold 12 and exhaust manifold
The exhaust passage 18 on the downstream side of 13 is connected by an exhaust gas recirculation (EGR) passage 19. The reflux control valve 37 is a butterfly valve,
It is provided in the EGR passage 19 and is controlled to open and close by a motor (not shown) via a control circuit 41 to change the exhaust gas recirculation amount (EGR rate). The opening sensor 38 is a variable resistance type position sensor, and outputs a signal according to the opening degree of the recirculation control valve 37.

An oxygen concentration sensor 39 is provided on the exhaust passage 18 closer to the exhaust manifold 13 than the connecting portion of the EGR passage 19. The oxygen concentration sensor 39 outputs a signal according to the concentration of oxygen contained in the exhaust gas (that is, the air-fuel ratio). That is, this sensor 39 shows the relationship between the applied voltage and the output current as shown in FIG. 3 (a) when the oxygen concentration is constant,
By fixing the applied voltage to V ₀ , a current proportional to the oxygen concentration is output as shown in FIG. 3 (b).

The distributor 25 is rotationally driven by a cam shaft (not shown) and supplies a high current to each spark plug 21, 22, 23, 24. The reference position sensor 26 is the distributor 25.
It is attached to and outputs a reference position signal every 720 ° CA (crank angle). The crank angle sensor 27 is attached to the distributor 25 and outputs a signal every 30 ° CA (crank angle).

The control circuit 41 includes a microcomputer, detects the torque difference of each cylinder based on the signals from the sensors 16, 26, 27, 38, 39, and calculates the fuel injection amount for each cylinder, as described later. As shown in FIG. 2, the control circuit 41 includes a central processing unit (CPU) 42, a memory 43, and an input port 44.
And an output port 45, which are connected by a bus 46. Each sensor 16, 26, 27, 38, 39 is connected to an input port 44 and an output port 45 of the fuel injection valve 31, 32, 33, 34.

FIG. 4 shows a routine for detecting an output torque difference between the cylinders by the control circuit 41. This routine is interrupted and executed at every fixed crank angle.

In step 101, the current cylinder is set to the compression top dead center (TD
C) is determined. This determination is made based on the output signals from the reference position sensor 26 and the crank angle sensor 27, as is well known in the art. That is, the reference position signal is output, for example, at the compression TDC of the first cylinder, and 180 ° CA, 360 ° C. from the detection of the reference position signal.
A, After 540 ゜ CA, the third, fourth and second cylinders are compressed T
Located in DC. If the predetermined cylinder is not currently in the compression TDC, execution of step 101 terminates this routine immediately, but if the predetermined cylinder is in the compression TDC, step 102 is executed.

In step 102, 180 ° CA after the compression TDC of the cylinder,
That is, the predetermined time T180i in the explosion stroke is calculated based on the output signal of the crank angle sensor 27 and the timer. The required time T180i is proportional to the reciprocal of the output torque of the cylinder. In step 103, the cylinder counter i is incremented by 1, and in step 104, it is determined whether or not the calculation of the required time T108i in step 102 has been completed for all cylinders. If step 102 has been completed for all cylinders, the routine proceeds to step 105, but if not completed, this routine is immediately terminated. In this embodiment, since the engine has four cylinders, it may be determined in step 104 whether the cylinder counter i has exceeded four. Note that 1, 2, 3, and 4 of the cylinder counter i indicate the ignition order, and correspond to the first, third, fourth, and second cylinders, respectively.

In step 105, the average required time T180AV at 180 ° CA of the explosion stroke of all cylinders is calculated. And step 10
In 6, for each cylinder, the ratio Ki of the required time for the 180 ° CA period of that cylinder and the average required time for the 180 ° CA period of all cylinders is obtained. That is, the ratio Ki indicates the ratio between the torque of the cylinder and the average value of the torque of all cylinders.

At step 107, it is judged if the fuel supply is currently cut off (fuel cut). Throttle sensor 16
Thus, when it is detected that the throttle valve 15 is substantially fully closed, and the engine speed is higher than a predetermined value, it is determined that the fuel is currently being cut off. Executed but throttle valve 15
Was judged not to be in the fuel cut time when it was not fully closed,
Next, step 111 and subsequent steps are executed.

In step 121, the ratio Ki is integrated for each cylinder to obtain an integrated value SKFCi, and the cycle counter Jf is set to 1
Is incremented only. That is, the integrated value SKFCi is
The ratio Ki of the time required for the explosion stroke of each cylinder and the average time required for the explosion stroke of all cylinders during fuel cut is added up. The magnitude relationship of the integrated value SFCFi of each cylinder during fuel cut means an error in the angle detection of the crank angle sensor because each cylinder is not in a combustion state.

In step 122, it is determined whether or not the cycle counter Jf has reached 50, that is, in step 121, whether or not the ratio Ki has been integrated for 50 cycles. If the integration for 50 cycles has not been completed, the routine proceeds to step 117, where the cylinder counter i is set to 1, and this routine ends. Thereafter, the ratios Ki (step 106) are obtained again for all the cylinders. In step 122, the cycle counter Jf becomes 50
If so, in step 123, the integrated value SKFCi
Is replaced with the integrated value SKFi, and the integrated value SKFCi and the cycle counter Jf are cleared to zero.

In step 111, the ratio Ki of each cylinder during fuel supply
Are integrated to obtain an integrated value SKi, and the cycle counter J is incremented by one. Integrated value of each cylinder
SKi corresponds to the output torque of each cylinder,
Includes an error in the angle detection of the crank angle sensor. Before the counter J reaches 50, the process proceeds from step 112 to step 117, in which the cylinder counter i is set to 1 and this routine ends, but if the counter J has reached 50, the process proceeds to step 117.
113 is executed. That is, the difference between the integrated values SK _i and SK _i-1 during fuel supply and the difference between the integrated values SK Fi and SKF _i-1 during fuel cut are calculated for two cylinders in which the explosion strokes are continuous, and these differences are further calculated. (SKi-SKi- ₁ ) and the difference (SKFi-
SKF _i-1 ) and the change amount DSK _i . This change amount DSKi
Represents the amount of torque drop in that cylinder, and the angle detection error of the crank angle sensor has been removed.

In step 114, it is determined whether or not the amount of change DSKi is equal to or greater than a determination value. If the change amount DSKi is equal to or greater than the judgment value,
In step 115, the fuel injection correction coefficient KTAUi is increased by 0.05, and if the change amount DSKi is smaller than the determination value, step 115 is not executed and the current fuel injection correction coefficient KTAUi is maintained. Steps 114 and 115 are executed for all the cylinders, whereby the fuel injection amount is increased and corrected for the cylinders whose output torque is smaller than those of the other cylinders. The fuel injection amount TAUi is calculated by TAUi = FAF × KTAUi × αi × TP (1). Where FAF is the feedback coefficient,
αi is the correction coefficient, TP is the basic injection amount, and the basic injection amount TP
Is determined by the ratio between the intake air amount and the engine speed, as is well known in the art.

In step 116, the integrated value SKi and the cycle counter J are set to 0.
Is cleared, and in step 117, the cylinder counter i is set to 1.

However, in this embodiment, first, one cycle (720 ° CA)
180 ゜ CA period of the explosion stroke of each cylinder and 180 averages of all cylinders
比 The ratio Ki to the CA period is calculated, and the integrated values SKi and SKFi for 50 cycles during fuel supply or fuel cut
Is required. This integrated value is updated every 50 cycles. Integrated value for the two-cylinder explosion stroke is continuous then SKi, SK _i-1 of the difference _{(SKi-SK i-1)} and the integrated value SKFi, SKF _i-1
(SKFi−SKF _i−1 ) is calculated, and if the change amount DSKi of these differences is equal to or larger than the determination value, the output torque of the cylinder corresponding to the cylinder counter is determined to be too small, and the fuel injection amount is increased. .

As described above, the magnitude relationship of the integrated value SKFi of each cylinder during the fuel cut indicates an error in the angle detection of the crank angle sensor because each cylinder is not in a combustion state. Therefore, if the torque generated during the explosion stroke is uniform in each cylinder, the magnitude relationship of the integrated value SKi of each cylinder during fuel supply is substantially the same as the magnitude relationship of the integrated value SKFi of each cylinder during fuel cut. . That is, the change amount DSKi is
This indicates whether the output torque of the cylinder is too small with respect to the output torque of the other cylinders. In the present embodiment, in steps 114 and 115, the fuel injection correction coefficient KTAUi is increased and the fuel injection amount is increased for the cylinder whose output torque is too small. As a result, the output torque difference is substantially removed for all cylinders, and the output torques for all cylinders are adjusted to be uniform.

FIG. 5 shows a routine for controlling the air-fuel ratio of exhaust gas. This routine is executed by being interrupted for every predetermined crank angle as in the output variation detecting routine of FIG.

In step 131, the air-fuel ratio A / F is read from the oxygen concentration sensor 39, and the air-fuel ratio A / F is compared with the target value in step 132. If the air-fuel ratio A / F is above the target value, step 1
At 33, when the feedback coefficient FAF is increased by the predetermined value αf and the air-fuel ratio A / F is smaller than the target value,
In step 134, the feedback coefficient FAF is the predetermined value β
It can be reduced by i. Then feedback coefficient
FAF increases or decreases according to the magnitude of the air-fuel ratio A / F, and the fuel injection amount is controlled by this (see equation (1)), and the air-fuel ratio A / F approaches the target value.

FIG. 6 shows an EGR control routine for controlling the opening degree of the reflux control valve 37. This routine is executed by interruption processing for each predetermined crank angle.

In step 201, the average effective pressure P _i previously stored in the memory 43 is read. In the present embodiment, this average effective pressure P _i is the work amount ΔP _i = P × ΔV between 5 ° CA for every 5 ° CA in the compression stroke and the explosion stroke of the first cylinder (P is the combustion pressure, Δ V can be obtained by obtaining and integrating the cylinder volume change amount for every 5 ° CA, and dividing this integrated value by the stroke volume V _h . In step 202, it is judged whether or not it is the intake TDC at present, and if it is not the intake TDC, this routine ends as it is, but if it is the intake TDC, steps 203 and thereafter are executed. In step 203, the average effective pressure P _{i for} 16 cycles is
Are stored in A (J) and the counter J is incremented by one. Before the counter J reaches 16, a negative determination is made in step 204, and this routine ends as it is. If the counter J reaches 16, the process proceeds from step 204 to step 205.

At step 205, each average effective pressure P in 16 cycles
The variation of _i (stored in step 203) or the variance S ² is calculated. The variance S ² is the square of the standard deviation, Required by. Next, at step 206, the counter J is cleared to 0. The variance S ² in step 207 is determined whether or not smaller than the set value, EGR opening degree coefficient KEGR at step 208 when the variance S ² is smaller than the set value αe
The EGR opening coefficient KEGR is decreased by βe in step 209 when the variance S ² is equal to or larger than the set value. However, the opening degree of the recirculation control valve 37 is set as large as possible within the limit that the variation in the combustion pressure between the cylinders is within a predetermined range.

As described above, according to this embodiment, first, the output fluctuation detection routine adjusts the output torque of each cylinder, that is, the combustion state to be uniform. If the output torque of all cylinders is not uniform, the lean limit (lean air-fuel ratio limit) is determined by the cylinder with the worst combustion condition. Therefore, considering the output torque difference between the cylinders, the air-fuel ratio slightly on the rich side of the lean limit Will be controlled. However, according to the present embodiment, since the output torque of each cylinder is uniform as described above, the lean limit is expanded, and the air-fuel ratio of the exhaust gas is made as lean as possible by the air-fuel ratio control routine of FIG. be able to. Therefore, the catalyst provided in the exhaust system can reduce the NO _X component in the exhaust gas and improve the fuel consumption.

Further, according to the present embodiment, the combustion state of each cylinder is made uniform, and the opening degree of the recirculation control valve 37 is controlled by the EGR control routine of FIG. 6 as long as the variation of the combustion state of each cylinder is within the predetermined range. Is maximized and the EGR rate is increased as much as possible. That is, the exhaust gas recirculation amount becomes sufficient, and the NO _X in the exhaust gas can be sufficiently reduced.

Further, the present embodiment is configured to use the output signal of one combustion pressure sensor 35 to control the opening degree of the reflux control valve 37. Therefore, the opening / closing control of the recirculation control valve 37 is simple, and the controllability does not deteriorate even if the engine speed increases. Further, since only one combustion pressure sensor 35 is required, the configuration is simple, and the whole apparatus is inexpensive.

In order to adjust the output torque of each cylinder to be uniform, it is not always necessary to control the fuel injection amount as in the above embodiment, and the ignition timing may be controlled for each cylinder.

〔The invention's effect〕

As described above, according to the present invention, the content of control of exhaust gas recirculation is simple, and a predetermined exhaust gas recirculation amount can be reliably obtained regardless of the engine speed. An exhaust gas recirculation control device having a simple structure and a low cost can be obtained.

[Brief description of drawings]

1 is a configuration diagram of the invention, FIG. 2 is a diagram showing an engine to which an embodiment of the present invention is applied, FIG. 3 (a) is a graph showing a relationship between an applied voltage and an output current of an oxygen concentration sensor, FIG. 3 (b) is a graph showing the relationship between the oxygen concentration and the output current of the oxygen concentration sensor, FIG. 4 is a flowchart of the output fluctuation routine, FIG. 5 is a flowchart of the air-fuel ratio control routine, and FIG. 6 is a flowchart of the EGR control routine. It is a flowchart. 19 …… Exhaust gas recirculation passage, 21,22,23,24 …… Spark plug, 31,32,33,34 …… Fuel injection valve, 35 …… Combustion pressure sensor, 37 …… Recirculation injection valve.

Claims (1)

(57) [Claims] 1. A recirculation control valve provided in an exhaust gas recirculation passage connecting an intake system and an exhaust system, a combustion pressure sensor provided in one cylinder, and means for detecting a difference in output torque of each cylinder,
A means for adjusting the output torque of each cylinder so that the output torque difference is substantially eliminated; and, after the output torque is adjusted, the recirculation according to the magnitude of the fluctuation of the combustion pressure of the one cylinder. An exhaust gas recirculation control device comprising: means for controlling the opening of a control valve.