JPH06336957A - Egr control device for diesel engine - Google Patents

Abstract

PURPOSE:To prevent EGR control from being influenced by the lowering of EGR flow detecting accuracy in a low rotation area and a low EGR flow area by performing feedback control only when the actual value of pressure differ ence between an EGR passage and an intake passage exceeds the limit value, and switching it to open control when the actual value becomes the limit value or less. CONSTITUTION:A computing means 31 computes the differential pressure objective value DELTA Pt according to the detection value of an operating condition, and a computing means 32 computes the correction quantity to the control command value to an actuator 25 for an EGR valve so that the differential pressure objective value DELTAPt and the differential pressure actual value DELTAPs of a sensor 30 coincide with each other. According to the judged result of a control area judged by a judging means, a determining means 34 determines the control command value to the actuator 25 for the EGR valve respectively using the correction quantity in a feedback control area and according to the opening objective value of the EGR valve corresponding to the detection value of the operating condition in an open control area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine EGR controller.

[0002]

NO emitted from a diesel engine
For the purpose of reducing x, an EGR device that suppresses combustion by recirculating a part of exhaust gas into intake air is adopted.

The required value of the exhaust gas recirculation amount (EGR flow rate) differs depending on the operating conditions, and depending on the operating conditions, the EG
Since R hinders the output performance of the engine, the target value of the EGR rate (= EGR flow rate / intake air flow rate) according to the operating conditions is set in advance so that the engine output performance and the exhaust performance are balanced. Then, by referring to this map of target values, the target EGR that matches the current operating conditions
The target EGR rate is converted into a control command value, which is applied to each actuator for the EGR valve and the intake throttle valve to control the opening degrees of the EGR valve and the intake throttle valve.

However, if the actual EGR rate deviates from the target value due to an operation error with respect to the control command value of each actuator for the EGR valve or the intake throttle valve or adhesion of carbon contained in the EGR gas to the EGR valve, Exhaust performance may deteriorate.

For this reason, in Japanese Patent Laid-Open No. 165656/1982, the actual EGR rate is detected for each constant traveling distance,
The control command value to the EGR valve actuator is feedback-controlled so that this coincides with the target value. A sensor for detecting the intake air flow rate and the EGR flow rate is provided, the actual EGR rate is calculated from these sensor values, and if this is larger than the target value, the EGR valve opening becomes smaller, and vice versa. When is smaller than the target value, the control command value to the EGR valve actuator is corrected to the side where the EGR valve is opened.

[0006]

By the way, in order to detect the EGR flow rate in the above device, the passage is branched into two in the middle of the EGR passage, and one of the branch passages is provided with a venturi portion. The differential pressure is taken out by the differential pressure transducer. Since the flow rate of the venturi section is determined by the flow passage area of the venturi section and the differential pressure across the venturi, the differential pressure across the venturi is converted to the EGR flow rate by utilizing this relationship.

However, under operating conditions such as a low rotation speed range and a low EGR flow rate range, the differential pressure across the venturi portion becomes small, and the EGR flow rate cannot be detected accurately.
When the EGR rate is feedback-controlled by using the detection value of the EGR flow rate which is not accurate, the feedback control accuracy is rather deteriorated.

Therefore, according to the present invention, the feedback control is performed only when the measured value of the pressure difference between the EGR passage and the intake passage exceeds a predetermined limit value, and when the measured value becomes equal to or less than the limit value, the control is switched to the open control to reduce the rotation speed. Range and low EGR
It is an object of the present invention to eliminate the influence on the EGR control due to the decrease in the detection accuracy of the EGR flow rate in the flow rate range.

[0009]

According to the present invention, as shown in FIG. 1, an EGR which connects an exhaust passage 21 and an intake passage 22 with each other.
The passage 23 and the EGR valve 2 that opens and closes the EGR passage 23
4, an actuator (for example, a duty control valve) 25 capable of variably adjusting the opening degree of the EGR valve 24, and a valve 26 that is located upstream of the connection between the EGR passage 23 and the intake passage 22 and throttles the intake air. An actuator 27 capable of adjusting the opening degree of the intake throttle valve 26 in multiple stages, and a detected value of operating conditions (for example, engine speed Ne and engine load L).
means 28 for controlling the intake throttle valve actuator 27 so that the intake throttle valve opening degree corresponds to p);
A means 29 for calculating a target opening value of the GR valve 24 in accordance with the detected value of the operating condition, and a sensor 30 for actually measuring the differential pressure between the exhaust passage 21 and the intake passage 23 downstream of the intake throttle valve 26.
And means 31 for calculating the target value ΔPt of the differential pressure according to the detected value of the operating condition, and the EGR valve actuator 25 so that the target differential pressure value ΔPt and the actual differential pressure value ΔPs match. Means 32 for calculating a feedback correction amount for the control command value to the
If the measured differential pressure value ΔPs exceeds the differential pressure limit value ΔP ₀ by comparing s with a predetermined differential pressure limit value ΔP ₀ , it is in the feedback control range, and the measured differential pressure value ΔPs is the differential pressure limit value ΔP 0. _{When the value is 0} or less, each means 33 that determines that the control range is the open control range, and the feedback control amount is used in the feedback control range based on the determination result,
Further, when the open control range is reached, the EGR valve opening target value corresponding to the detected value of the operating condition is set to the EGR valve opening target value.
Means 34 for determining a control command value for the valve actuator 25 is provided.

In a second aspect of the invention, when the measured differential pressure value ΔPs and the differential pressure target value ΔPt match in the feedback control range, the reference value of the EGR valve opening at the time of standard exhaust pressure and the actual EGR valve opening. The difference from the degree is calculated as a correction amount and is held, and the opening target value of the EGR valve 24 in the open control range is corrected by this correction amount.

[0011]

In the first aspect of the invention, the measured differential pressure value ΔPs is the differential pressure limit value Δ.
When P ₀ is exceeded, the measured differential pressure value ΔPs is equal to the differential pressure target value Δ
By feedback-controlling the control command value given to the EGR valve actuator 25 so as to match Pt,
Even when the exhaust pressure rises due to the accumulation of particulates (exhaust particles) in the aftertreatment device provided in the exhaust passage 21, the target EGR rate according to the operating conditions can be obtained. Also,
No intake air flow sensor is required.

On the other hand, the measured differential pressure value ΔPs is the differential pressure limit value ΔP
_When it becomes ₀ or less, it is determined that the differential pressure is not accurately measured, and the open control is switched to the exhaust passage 21.
Is not affected by the measurement error associated with the actual measurement of the differential pressure between the intake throttle valve 26 and the intake passage 23 downstream of the intake throttle 23.

In the second invention, the difference between the reference value of the EGR valve opening at the time of standard exhaust pressure and the actual EGR valve opening in the feedback control region is calculated as a correction amount, and this correction amount is used for open control. When the opening target value of the EGR valve is corrected, even when the exhaust control is performed by the post-treatment device provided in the exhaust passage, the EGR is performed regardless of the increase in the exhaust pressure during the open control as in the feedback control. The rate is kept constant.

[0014]

In FIG. 2, an EGR passage 3 connecting the exhaust passage 1 and the intake passage 2 is provided with an orifice 4 at a connecting portion with the intake passage 2 and an E near the connecting portion with the exhaust passage 1.
An EGR valve 5 that opens and closes the GR passage 3 is provided.

The EGR valve 5 has its valve lift (a valve opening equivalent value) adjusted by a duty control valve (actuator) 6 to give a duty ratio (ON time ratio per constant time period) to the control valve 6. The valve lift increases proportionally. The higher the duty ratio, the more vacuum pump (driven by the engine) than atmospheric pressure 7
The ratio of introducing a constant negative pressure from the EGR valve increases, the control negative pressure to the working chamber 5A of the EGR valve increases, and the valve lift increases.

Similarly, the intake throttle valve 8 provided upstream of the connection between the EGR passage 3 and the intake passage 2 has its valve opening adjusted by the duty control valve 9, and has three stages (for example, 20 degrees, 30 degrees, 80 degrees). EGR
Even if the lift of valve 5 is the same, the larger the differential pressure across the valve, the more E
Since the GR flow rate increases, if the control negative pressure to the diaphragm actuator 10 is increased and the intake throttle valve 8 is closed, E
The differential pressure across the GR valve 5 increases and the EGR flow rate increases.

However, since the throttle valve 6 also controls the flow rate of air taken into the engine, the target EGR rate and the intake throttle valve opening characteristic are set so as not to impair the original output performance of the engine. As shown in FIG. 3, it is determined according to operating conditions. In FIG. 3, as the engine load (for example, the opening degree of the injection pump lever) Lp in the EGR control region becomes smaller, and as the engine speed (obtained from the rotation speed of the injection pump) Ne becomes smaller, the target EGR rate becomes larger. Therefore, according to this target EGR rate, the EGR flow rate flows as shown by the broken line.

Since FIG. 3 shows the characteristics when the exhaust system does not have a passage resistance, the post-treatment device 12 such as a filter for collecting the particulates in the exhaust passage 1 in FIG. When provided, the exhaust pressure rises as the amount of collected particulate matter in the post-treatment device 12 increases even under the same operating conditions. Therefore, the EGR flow rate increases as the exhaust pressure rises, and the actual EGR rate increases. Is out of the target value.

As a measure against this exhaust, a pressure sensor (absolute pressure sensor) 1 provided in each of the EGR passage 3 and the intake passage 2
3, 14 the differential pressure across the orifice 4 (this differential pressure
(Referred to as differential pressure) is measured, and the control unit 11 including a microcomputer corrects the duty ratio given to the control valve 6 so that the measured value of the EGR differential pressure matches the target value of the EGR differential pressure determined according to the operating conditions. By doing so, the EGR rate can be kept constant even if the exhaust pressure rises. FIG. 4 shows the effect of increasing the exhaust pressure above the standard exhaust pressure (exhaust pressure without the aftertreatment device; 5 mmHg in the figure) under the same operating conditions. The reason why the target is set is that, as shown in the second stage of FIG. 4, if the EGR differential pressure is constant even if the exhaust pressure increases, the EGR rate becomes constant. The two pressure sensors 13 and 14
Alternatively, a differential pressure sensor that directly detects the differential pressure across the orifice 4 may be used.

However, the slope of the EGR differential pressure with respect to the EGR rate becomes lower as the rotation speed becomes lower as shown in FIG.
Since the R ratio becomes smaller, the actual EGR differential pressure cannot be accurately detected in the low rotation speed region and the low EGR ratio region. Even if the EGR rate changes in the low rotation range and the low EGR rate range, the measured value of the EGR differential pressure remains unchanged before and after the change of the EGR rate.

Although the EGR differential pressure is increased by reducing the flow passage area of the orifice 4, the flow passage area of the orifice 4 is reduced because the required maximum EGR flow rate must be made to flow. However, there is a limit, and it is difficult to create the required EGR differential pressure in all operating ranges where EGR is required.

Therefore, in this example, a limit value of the EGR differential pressure is set so that the required accuracy can be secured, and if the measured value of the EGR differential pressure is equal to or higher than this limit value, the measured value of the EGR differential pressure depends on the operating conditions. Feedback control of the duty ratio (control command value) given to the control valve 6 so as to match the target value
When the measured value of the EGR differential pressure becomes less than or equal to the limit value, the feedback control is stopped and the open control is switched to.

In order to control the intake throttle valve 8 in three stages, a map containing the intake throttle valve opening characteristic of FIG. 3 is given in advance, and this map is calculated from the engine speed Ne and the engine load Lp. By referring to this, the throttle valve opening degree in the region to which the operating condition determined by the rotation speed and the detected value of the load belongs can be obtained, and this can be output to the control valve 9 by changing it into the duty ratio.

FIG. 6 is a flow chart for controlling the duty ratio applied to the control valve 6.

First, the measured value ΔPs of the EGR differential pressure is read from the signals of the two pressure sensors 13 and 14, and this is compared with a predetermined limit value (constant value) ΔP _{0 of the} EGR differential pressure (see FIG. Steps 1 and 2 of 6, ΔP
If s> ΔP ₀ , it is in the feedback control region. Conversely, if ΔPs ≦ ΔP ₀ , it is in the open control region. When the feedback control region and the open control region are shown in the operating region with the rotation speed Ne and the load Lp as parameters, the open control region has a low rotation region and a low EG as shown in FIG.
The EGR differential pressure, which is a combination of the R rate range (which is also a low EGR flow rate range) and corresponds to the boundary line between the feedback control range and the open control range, is the limit value ΔP ₀ .

By giving a region map having the contents of FIG. 8 in advance and referring to this map from the rotational speed Ne and the load Lp, it is determined whether the current operating condition is in the feedback control region or the open control region. You may decide to judge. In the feedback control region, the target value ΔPt of the EGR differential pressure is obtained from the rotational speed Ne and the load Lp with reference to the map having the content of FIG. 9 (steps 3 and 4 in FIG. 6). The map of the target value ΔPt is obtained by replacing the characteristic of the target EGR rate of FIG. 3 with the characteristic of the EGR differential pressure using the relationship of FIG.

The target value ΔPt and the measured value ΔPs are compared. If ΔPt ≠ ΔPs, the measured value ΔPs is the target value ΔPs.
The duty ratio to the control valve 6 is corrected so as to match Pt (steps 5 and 6 in FIG. 6). For example, ΔPs> Δ
If it is Pt, it is determined that the EGR flow rate is increasing due to the increase of the exhaust pressure, and the EGR flow rate is decreased. Therefore, as shown in the subroutine of FIG. 7, from the duty ratio Dt to the constant value ΔD.
The value obtained by subtracting t is newly set as the duty ratio Dt so that the EGR valve 5 is closed (steps 21, 22, and 23 in FIG. 7). ΔPs <ΔP
At t, the duty ratio is increased and corrected, and the EGR valve 5 is driven to the open side (steps 21, 24 and 23 in FIG. 7).

On the other hand, in the open control range, the rotation speed N
The target lift value Ht of the EGR valve is obtained from e and the load Lp with reference to the map having the contents of FIG. 10 (steps 7 and 8 in FIG. 6). The map of the target value Ht shows the target EGR rate characteristic of FIG. 3 at the bottom of FIG. 4 at the time of standard exhaust pressure (exhaust pressure is 5 m.
The relationship between the EGR rate and the EGR valve lift at mHg) is used to replace the EGR valve lift characteristic.

The target lift value Ht of this EGR valve is shown in FIG.
Is converted to a duty ratio using a table containing
This converted duty ratio D _OP is output to the control valve 6 (steps 9, 10, 11 in FIG. 6).

As described above, when the measured value of the EGR differential pressure exceeds the predetermined limit value of the EGR differential pressure, the EGR
By performing feedback control of the duty ratio to the control valve 6 so that the measured value of the differential pressure matches the target value, even if the particulate pressure is accumulated in the post-processing device 12 and the exhaust pressure rises, the target according to the operating conditions can be obtained. The EGR rate is obtained.

Further, since the EGR differential pressure is used as the target value instead of the EGR rate, the intake air flow rate sensor is unnecessary unlike the conventional example.

On the other hand, when the measured value of the EGR differential pressure becomes less than or equal to the limit value of the EGR differential pressure, it is determined that the EGR differential pressure cannot be accurately measured, and the open control is switched to reduce the EGR differential pressure. Also, it is not affected by the measurement error caused by actually measuring the EGR differential pressure in the low EGR rate range.

FIG. 12 shows a second embodiment. When the aftertreatment device 12 is provided in the exhaust passage 1 and the open control is performed even though the measurement accuracy of the EGR differential pressure is not good, the EGR flow rate increases due to the increase in exhaust pressure, and the amount of smoke exhausted by that amount increases. Therefore, it is necessary to set the target EGR rate so that the target value of the EGR flow rate becomes small in consideration of this increase in smoke.
The effect of NOx reduction due to is reduced.

Therefore, in this example, the EGR valve lift is different if the exhaust pressure is different even if the EGR differential pressure is the same (see the bottom of FIG. 4). Lift reference value H ₀ and actual EG
The difference from the R valve lift Hc is calculated as a correction amount ΔH (= Hc−H ₀ ), and the lift target value Ht of the EGR valve is corrected during the open control with the correction amount ΔH.

Specifically, at standard exhaust pressure (exhaust pressure is 5 mmHg
13), the actual value Hc of the EGR valve lift is obtained from the duty ratio Dt given to the control valve 6, and the lift reference value H ₀ of the EGR valve is shown in FIG. Table is obtained by referring to each of them when ΔPs = ΔPt, and the difference between them is stored as a correction value ΔH (= Hc−H ₀ ) (steps 31, 32, 33 in FIG. 12). , 34), the value obtained by subtracting the correction amount ΔH from the EGR valve lift target value Ht is newly set as the target value Ht (step 35 in FIG. 12).

For example, during feedback control, Hc>
If the actual EGR valve lift does not become higher than the target value than H ₀ and the EGR differential pressure deviates to the larger side, it means that the exhaust pressure is high even under the same operating conditions. The lift target value Ht of the EGR valve is corrected so as not to deviate to the side where the pressure increases, and conversely, when Hc <H ₀ , the target value Ht is corrected so as to increase. Note that FIG. 10 also shows the characteristics at the time of standard exhaust pressure.
Since it has the same characteristics as above, the value referring to the map of the target value Ht may be replaced with the reference value H ₀ .

Thus, in the feedback control range, the difference between the lift reference value H ₀ of the EGR valve and the actual EGR valve lift Hc at the time of standard exhaust pressure is calculated as the correction amount ΔH,
By correcting the target value Ht of the EGR valve lift at the time of open control with this correction amount ΔH, when the exhaust pressure rises by the post-processing device 12 provided in the exhaust passage in the open control region as well as the feedback control region. However, the EGR rate can be kept constant regardless of the increase in exhaust pressure.

When the aftertreatment device is provided in the exhaust passage and the open control for keeping the EGR valve lift constant under the same operating condition is performed in the entire operating range, the EGR flow rate increases due to the increase in exhaust pressure. As described above, since the particulate matter increases, it is necessary to set the EGR flow rate to a small value with a margin so that the particulate matter increase when the exhaust pressure rises does not pose a problem.
In the embodiment, the margin allowance in consideration of the increase in the particulates becomes unnecessary for the feedback control area,
Since the target value of the R flow rate can be increased, NOx
Can be reduced. In the second embodiment, the target value of the EGR flow rate can be increased even in the open control range.
NOx can be further reduced as compared with the embodiment.

In the embodiment, the intake throttle valve 8 is set to 20 degrees and 30 degrees.
It is controlled in three steps of 80 degrees and 20 degrees, 30 degrees
For actual throttle valve opening values such as
Needless to say, the appropriate value varies depending on the engine model and throttle valve specifications.

[0040]

According to the first aspect of the present invention, when the differential pressure measured value between the exhaust passage and the intake passage downstream of the intake throttle valve exceeds the limit value, feedback control with the differential pressure as a target value is performed.
When the differential pressure becomes equal to or lower than the limit value, the feedback control is stopped and switched to the open control.Therefore, in the feedback control region, even when the particulate matter accumulates in the aftertreatment device provided in the exhaust passage and the exhaust pressure increases, A target EGR rate according to operating conditions can be obtained, and unlike the conventional example, an intake air flow rate sensor is not required, and the differential pressure is actually measured in a low rotation range or a low EGR rate range which is an open control range. It is not affected by the measurement error associated with.

In a second aspect of the invention, when the measured differential pressure value and the differential pressure target value match in the feedback control range, the opening reference value of the EGR valve at the time of standard exhaust pressure and the actual EGR valve opening degree are set. The difference between is calculated as a correction amount and held,
Since the target opening value of the EGR valve in the open control range is corrected by this correction amount, even in the open control range, even when the exhaust pressure is increased by the exhaust aftertreatment device, as in the feedback control range. The EGR rate can be kept constant regardless of the increase in the exhaust pressure.

[Brief description of drawings]

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

FIG. 2 is a system diagram of an EGR control device.

FIG. 3 is a characteristic diagram of a target EGR rate and an intake throttle valve opening degree according to operating conditions.

FIG. 4 is a graph showing NO with respect to EGR rate when exhaust pressure is increased.
FIG. 3 is a characteristic diagram of x discharge amount, EGR differential pressure, intake air flow rate, and EGR valve lift.

FIG. 5: EGR when changing the number of revolutions at standard exhaust pressure
It is a characteristic view showing the relationship between a rate and EGR differential pressure.

FIG. 6 is a flowchart showing the control contents of the control unit 11.

FIG. 7 is a flowchart showing the contents of correction of the duty ratio in the feedback control region.

FIG. 8 is a region diagram showing a feedback control region and an open control region.

FIG. 9 is a characteristic diagram showing map contents of a target value ΔPt of EGR differential pressure.

FIG. 10 is a characteristic diagram showing map contents of a lift target value Ht of an EGR valve.

FIG. 11 is a characteristic diagram showing the relationship between the lift target value Ht of the EGR valve and the duty ratio D _OP .

FIG. 12 is a flowchart showing the control contents of the second embodiment.

FIG. 13 is a characteristic diagram showing a map content of a lift reference value H ₀ of the EGR valve at the time of standard exhaust pressure.

FIG. 14 is an actual EGR valve lift Hc and duty ratio D.
It is a characteristic view which shows the relationship of t.

[Explanation of symbols]

 1 Exhaust Passage 2 Intake Passage 3 EGR Passage 5 EGR Valve 6 Duty Control Valve (EGR Valve Actuator) 8 Intake Throttle Valve 9 Duty Control Valve (Intake Throttle Valve Actuator) 11 Control Unit 13, 14 Pressure Sensor 21 Exhaust Passage 22 Intake Passage 23 EGR Passage 24 EGR valve 25 EGR valve actuator 26 Intake throttle valve 27 Intake throttle valve actuator 28 Throttle valve control means 29 EGR valve opening target value calculation means 30 Differential pressure sensor 31 Differential pressure target value Differential pressure means 32 Feedback Correction amount calculation means 33 Control area determination means 34 Control command value determination means

Claims (2)

[Claims] 1. An EGR passage that connects an exhaust passage and an intake passage, an EGR valve that opens and closes the EGR passage, and an EG
An actuator that can variably adjust the opening of the R valve, a valve that is located upstream of the connection between the EGR passage and the intake passage, and throttles the intake air, and an actuator that can adjust the opening of the intake throttle valve in multiple stages. And means for controlling the intake throttle valve actuator so that the intake throttle valve opening degree corresponds to the detected value of the operating condition, and the opening target value of the EGR valve is calculated according to the detected value of the operating condition. Means, a sensor for actually measuring the differential pressure between the exhaust passage and the intake passage downstream of the intake throttle valve, a means for calculating a target value of the differential pressure according to the detected value of the operating condition, and a differential pressure target. A means for calculating a feedback correction amount for the control command value to the EGR valve actuator so that the measured value and the measured differential pressure match, and the comparison between the measured differential pressure and a predetermined differential pressure limit value. Differential pressure measurement Is in the feedback control range when the differential pressure exceeds the differential pressure limit value, and is in the open control range when the measured differential pressure value is less than or equal to the differential pressure limit value. Means for determining a control command value for the EGR valve actuator by using the feedback correction amount and in accordance with the opening target value of the EGR valve according to the detected value of the operating condition when the open control range is reached. An EGR control device for a diesel engine characterized by the above. 2. The difference between the reference value of the EGR valve opening and the actual EGR valve opening at the time of standard exhaust pressure is corrected when the actually measured differential pressure and the target differential pressure match in the feedback control range. 2. The EGR control device for a diesel engine according to claim 1, wherein the target value of the opening degree of the EGR valve in the open control range is corrected with this correction amount calculated and held as the amount.