JPH0816460B2 - Exhaust gas recirculation control device for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application" The present invention relates to exhaust gas recirculation (EGR) of a diesel engine.
Regarding the control device.

"Prior art" Generally speaking, the EGR system is designed to suppress the NOx generation by putting an inert exhaust gas into the combustion chamber to lower the combustion temperature of the air-fuel mixture. If the amount of EGR is too small, the amount of NOx reduction is small, and conversely EG
If the amount of R is too large, combustion becomes unstable and HC increases.
Unlike a gasoline engine, a diesel engine does not have a throttle valve, so the intake air amount is not controlled according to the load of the engine, and the lower the load of the engine, that is, the smaller the fuel injection amount, the more the air becomes excessive.

Conventionally, the EGR system of a diesel engine indirectly detects the injection amount for each engine speed with a lever opening sensor, and according to the engine speed and the lever opening of the pump, that is, the EGR system according to the engine load. The amount was determined and the opening of the recirculation amount control valve in the EGR passage was controlled. However, the accuracy of correspondence between the injection amount and the lever opening / rotation speed of the pump is poor, and the variation in the injection amount detected by the lever opening sensor is large, so the EGR amount deviates from the target air-fuel ratio (A / F). There was a problem that the air volume became large and the amount of smoke or HC increased due to an insufficient amount of EGR, and that the amount of air became excessive when the amount of EGR was too small and the NOx reduction effect was small.

Incidentally, the conventional Japanese Patent Laid-Open Publication No. 55-7964 discloses an invention in which the EGR amount is controlled according to the air-fuel ratio on the air excess side only by the output of the air-fuel sensor mounted on the exhaust pipe. Since the signal from the pump is not taken into consideration, there is a problem that the EGR amount control is delayed due to the variation in the fuel injection amount.

"Problems to be Solved by the Invention" The present invention has been made in view of the above problems, and controls the recirculation amount in a state where both the error of the fuel injection amount and the error of the recirculation amount are eliminated. Thus, it is an object of the present invention to provide an exhaust gas recirculation control device that can quickly obtain a target recirculation amount.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an exhaust gas refueling system for a diesel engine, which supplies fuel to a combustion chamber according to the rotational speed and load of the diesel engine by an injection pump (8). In the circulation control device, the recirculation amount from the exhaust pipe (3) to the intake pipe (2) is arranged in the exhaust gas recirculation passage (4) connecting the exhaust pipe (3) and the intake pipe (2). Recirculation control valve (5)
And a rotation speed detection means (9) for detecting the rotation speed of the engine
A load detecting means (10) for detecting the load of the engine; an oxygen concentration detecting means (12) provided in the exhaust pipe (3) for detecting the oxygen concentration in the exhaust gas; and performing the recirculation. Determining means (step 101) for determining whether or not the rotation speed detecting means (9) and the load detecting means (10) are used when it is determined by the determining means (step 101) that the recirculation is performed. Recirculation target air-fuel ratio calculation means (step 110) for calculating the target air-fuel ratio during recirculation based on each detected value, and recirculation calculated by this recirculation target air-fuel ratio calculation means (step 110) The recirculation amount control valve (5) so as to reduce the difference between the target air-fuel ratio at the time of recirculation and the actual air-fuel ratio at the time of recirculation measured based on the detection value of the oxygen concentration detection means (12). Recirculation amount control means to control (step 11
3, 114, 116) and the rotation speed detection means (9) when it is determined by the determination means (step 101) that the recirculation is not performed.
And, based on each detection value of the load detection means (10),
Non-recirculation target air-fuel ratio calculation means (step 104) for calculating the non-recirculation target air-fuel ratio, and non-recirculation target air-fuel ratio calculation means (step 104)
Error of the fuel injection amount obtained from the difference between the target air-fuel ratio at the time of non-recirculation calculated by and the actual air-fuel ratio at the time of non-recirculation measured based on the detection value of the oxygen concentration detection means (12). , An error calculating means (step 105) for calculating an error of at least one of the rotational speed and the load, and the error of the recirculation amount control valve (5) according to the error calculated by the error calculating means (step 105). An exhaust gas recirculation control device for a diesel engine, which comprises a correction means (step 108) for correcting the control amount.

The reference numerals in the parentheses of the above means indicate the correspondence with the specific means of the embodiments described later.

[Operation] According to the above configuration, when the actual injection amount supplied to the combustion chamber by the injection pump becomes excessive or excessively smaller than the target injection amount, it is detected as an injection amount error. Since it is reflected as a load error or a rotation speed error, the exhaust gas recirculation amount is accurately corrected according to the injection amount.

[Example] Hereinafter, a first example of the present invention will be specifically described with reference to the accompanying drawings.

In FIG. 1 showing an exhaust gas recirculation control device for a diesel engine according to the present embodiment, 1 is an engine body, 2 is an intake pipe, and 3 is an exhaust pipe for discharging exhaust gas from the engine body. . The engine body 1 includes an exhaust pipe 3 and an intake pipe 2
And an exhaust gas recirculation passage 4 for re-injecting the exhaust gas, and a recirculation amount control valve (EGR amount control valve) 5 for controlling the exhaust gas recirculation amount is installed in the passage, 8
Lean sensor which is the output of the rotation speed sensor 9 and the output of the lever opening sensor 10 and the air-fuel ratio sensor attached to the exhaust pipe 3.
In accordance with the output of 12, the negative pressure of the vacuum pump 7 controlled by the negative pressure control valve 6 is applied to the EGR amount control valve 5 to control the exhaust gas recirculation amount. The lean sensor 12 detects the residual oxygen in the exhaust gas to detect the air-fuel ratio on the excess air side. A signal to the negative pressure control valve 6 is sent to the ECU 11 according to the rotation speed of the pump 8 and the opening degree of the pump lever.
Is determined as a pulsed duty output.

[Operation] Next, in the method for correcting the variation in pump injection amount by the lean sensor 12 according to the present invention, first, the actual air-fuel ratio is detected by the lean sensor 12 mounted on the exhaust pipe 3, and the rotation speed of the pump 8 and the lever opening. Degree, the target air-fuel ratio is calculated, the injection amount error with respect to the lever opening is detected from the actual air-fuel ratio when the EGR is not executed, and the lever opening for realizing the target air-fuel ratio is calculated.
If there is a difference between the map values of the actual air-fuel ratio and the target air-fuel ratio, the lever opening error is reflected in the EGR amount control map, and the EGR amount control is performed based on the map that absorbed the injection amount error when executing EGR. .

A detailed flow of the above control will be described with reference to FIG. At step 101, it is judged from the engine water temperature, the lever opening (α), and the pump speed (N) whether or not the EGR execution condition is satisfied. When the EGR execution condition is satisfied, the routine proceeds to step 110, and when it is not satisfied, the step 102 is conducted. Go to. In step 102, it is determined whether or not the engine (E / G) state is in a predetermined stable state based on the change amount (ΔN) of the pump rotation speed within a predetermined time and the change amount (Δα) of the lever opening within the predetermined time. Then, if the engine is in the predetermined stable state, the routine proceeds to step 103, and if the engine is in the unstable state due to excess EGR amount, the routine proceeds to step 115. In step 103, the actual A / F (AFA) is measured according to the engine operating condition (pump speed and lever opening), and in step 104 the target A / F (AFT) is calculated according to the operating condition. In 105, the target A / F is calculated for each rotation speed from the values calculated in steps 103 and 104 above.
The lever opening error Δα is calculated from the difference between (AFT) and the actual A / F (AFA). It is determined in step 106 whether the lever opening error Δα is within a predetermined value a. If it is within a predetermined value, it is determined as normal, and if it exceeds the predetermined value, it is determined as abnormal and the process proceeds to step 115. In step 107, the lever opening error Δ
It is determined whether α is greater than or equal to a predetermined value b smaller than a, and b
In the following cases, the lever opening error Δα is assumed to be small, the learning value is set to “0”, and the routine proceeds to step 109. Lever opening error Δ
When α is α ≧ | Δα | ≧ b, in step 108, the lever opening error Δα calculated in steps 105 and 109 is set as the EGR amount map value, and the actual lever opening (α) is set as the lever opening error (Δα).
Is reflected in the form of correcting (α '← α ← Δα). Step
At 115, the EGR output value (Duty EGR) is set to “0” in order to cut the EGR according to the determination results at steps 101 and 102.

When it is determined in step 101 that the EGR execution condition is satisfied, steps 110 to 114 are performed. In step 110, the target A / F (AFTEGR) at the time of A / F feedback is set from the rotational speed (N) and the corrected accelerator opening (α '). In step 111, the actual A / F ( AFAEGR) is measured and the amount of deviation between the target A / F and the actual A / F during EGR is calculated in step 112. If the difference between the target value and the actual value (AFTEGR-AFAEGR) is positive, the EGR amount is insufficient. And proceed to step 113,
Increase the EGR amount (Duty EGR ← Duty EGR + ΔD), and conversely
If the difference between the target value and the measured value is negative, the EGR amount is excessive and the process proceeds to step 114 to decrease the EGR amount (Duty EGR ← Duty EGR-
ΔD), in step 116, the output operation of the EGR output value Duty EGR is performed. When the duty ratio of the EGR output value in step 116 is large, the pulse width is large and the time during which the negative pressure control valve 6 is open is long, so the negative pressure supplied to the EGR amount control valve 5 increases and the control valve 5 is opened greatly and the amount of EGR increases. As described above, the operations of steps 101 to 116 are repeated every predetermined period to execute the EGR amount control processing.

The control content according to this embodiment will be further described with reference to FIG. FIG. 3 (a) is a diagram showing the relationship between the lever opening (α), the EGR amount, and the target A / F during EGR execution, and FIG. 3 (b) shows the relationship between the lever opening and the A / F without EGR. A relationship diagram, FIG. 3 (c), shows a relationship diagram between the lever opening and the pump injection amount. The target characteristic of each control amount is that the target injection amount characteristic is a straight line q _T with respect to the lever opening (α).
The A / F target characteristic without EGR is shown as a straight line AFT, the target characteristic of the EGR amount is shown as a straight line EGRT, and the target A / F characteristic when EGR is executed is shown as a broken line A / F. When the injection amount characteristic with respect to the lever opening α of the pump deviates from the straight line q _A , the A / F characteristic without EGR has a relationship of the straight line AFA) due to excess air. However, if there is EGR, the target EGR amount and target A / F value are EGRO → EGRA, AF1 → A
Deviation from the original target value to F2, ΔEGR for a predetermined EGR amount
Only the weight is reduced, and the A / F also increases with the A / FA. For this reason, the EGR amount for the predetermined lever opening is insufficient, the air becomes excessive, and the NOx reduction amount becomes insufficient. In order to correct this pump injection amount error, in the present embodiment, the predetermined air-fuel ratio AFO without EGR is detected by the lean sensor, the lever opening deviation (Δα) with respect to the AFO is calculated, and the lever opening deviation ( Δα)
By reflecting the EGR amount map in the ECU 11 in the form of α ← α−Δα, the deviation of the EGR amount is corrected and the pump injection amount and the EGR amount are corrected.
The quantity correspondence is corrected to a predetermined relationship. As described above, according to the present embodiment, even if there is a deviation in the pump injection amount, it is detected by the lean sensor and corrected as a lever opening error to correct the EGR amount to correct the relationship between the pump injection amount and the EGR amount. Can be maintained at the target value.

"Other Embodiments" In the first embodiment of the present invention, the injection amount deviation is detected and corrected as an accelerator opening error, but it is also possible to detect and correct it as a rotational speed error of the EGR amount map. Needless to say, the second embodiment is shown in FIG. FIG. 4 is a diagram in which the lever opening and the rotational speed in FIG. 2 are exchanged, and in step 205, the fuel injection amount error for each lever opening is calculated between the target value (AFT) and the actual measurement value (AFA) of the lean sensor. The rotation speed error ΔN is obtained from the difference, and is reflected in the EGR amount map as N ′ ← N−ΔN as an error in the rotation speed direction in step 208. As described above, in the first embodiment, the pump injection amount error is detected and corrected as the lever opening error Δα.
The rotation speed error ΔN can be detected and corrected in the same manner as in the second embodiment.

Further, in the first and second embodiments, the lever opening is used as the load detecting means, but it goes without saying that the same effect can be exhibited even if the spill ring position, engine torque, etc. are substituted.

[Effect] As described above, the exhaust gas recirculation control device of the present invention has the above-mentioned configuration, and the error of the injection amount can be known during the non-recirculation, and this error is the target space during the recirculation. It is calculated as an error in at least one of the rotation speed and the load, which are parameters for calculating the fuel ratio. Then, since the control amount of the recirculation amount control valve is corrected according to the calculated error, the recirculation amount control valve is controlled by this corrected control amount during recirculation. Therefore, at the time of recirculation, it is possible to control the recirculation amount while eliminating both the injection amount error and the recirculation amount error, and as a result, the target recirculation amount can be obtained quickly and the emission deterioration (NOx generation ) And smoke can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, FIG. 2 is a flow chart showing the operation, and FIGS. 3 (a), (b),
(C) is a characteristic diagram for explaining the operation, and FIG. 4 is a flow chart showing the second embodiment. 1 ... Engine body, 2 ... Intake pipe, 3 ... Exhaust pipe, 4
...... Exhaust gas recirculation passage, 5 ...... Recirculation amount control valve, 6 ...
... Negative pressure control valve, 7 ... Vacuum pump, 8 ... Injection pump, 9 ... Rotation speed sensor, 10 ... Lever opening sensor,
11 …… ECU, 12 …… Lean sensor.

Claims (1)

[Claims] 1. An exhaust gas recirculation control device for a diesel engine, wherein an injection pump supplies fuel to a combustion chamber according to a rotational speed and a load of the diesel engine, in an exhaust gas recirculation passage connecting an exhaust pipe and an intake pipe. A recirculation amount control valve that is disposed and controls the recirculation amount from the exhaust pipe to the intake pipe, a rotation speed detection unit that detects the rotation speed of the engine, and a load detection unit that detects the load of the engine. An oxygen concentration detecting means provided in the exhaust pipe for detecting the oxygen concentration in the exhaust gas, a determining means for determining whether or not to perform the recirculation, and a determining means for performing the recirculation by the determining means. In this case, the recirculation target air-fuel ratio calculation means for calculating the target air-fuel ratio at the time of recirculation based on the detection values of the rotation speed detection means and the load detection means, and the recirculation target air-fuel ratio calculation To the means Therefore, in order to reduce the difference between the calculated target air-fuel ratio during recirculation and the actual air-fuel ratio during recirculation measured based on the detection value of the oxygen concentration detection means, the recirculation amount control valve is When the recirculation amount control means for controlling, and the determination means determines that the recirculation is not performed, based on the respective detection values of the rotation speed detection means and the load detection means, the target space during non-recirculation Based on the non-recirculation target air-fuel ratio calculation means for calculating the fuel ratio, the non-recirculation target air-fuel ratio calculated by the non-recirculation target air-fuel ratio calculation means, and the detection value of the oxygen concentration detection means. An error calculating means for calculating an error of the fuel injection amount obtained from the difference between the measured actual air-fuel ratio during non-recirculation as an error of at least one of the rotational speed and the load, and the error calculating means. According to the above error , The exhaust gas recirculation control device for a diesel engine, characterized in that it comprises a correction means for correcting the control amount of the recirculation amount control valve.