JPH06294355A - Exhaust circulation control device for diesel engine - Google Patents

Abstract

PURPOSE:To control an exhaust circulation rate minutely and accurately under various operation conditions, and eliminate influence of fluctuation of discharge pressure caused by an exhaust filter or the like. CONSTITUTION:An exhaust circulation control valve 2 which is controlled in its opening according to a duty ratio of a control signal is provided on an exhaust circulation passage, while an intake throttle valve is provided on an intake passage. The duty ratio is controlled so as to keep a target value of differencial pressure DELTAP1 in respect to an orifice which is provided on a joint part of the exhaust circulation passage and the intake passage in a low speed and low load area where the intake throttle valve shows an intermediate or small opening. The duty ratio is controlled so as to keep a target value of differencial pressure DELTAP2 in respect to the exhaust circulation control valve 2 in an intermediate speed and intermediate load area where the intake throttle valve is fully opened. The target value of DELTAP2 is calculated by searching a reference differencial pressure and a reference duty ratio from a map and obtaining the relation in respect to the present duty ratio in order to eliminate influence of discharge pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device for controlling an exhaust gas recirculation amount of a diesel engine according to engine operating conditions.

[0002]

2. Description of the Related Art Generally, in an exhaust gas recirculation system for a diesel engine, exhaust gas recirculation is controlled by switching an exhaust gas recirculation control valve installed in an exhaust gas recirculation passage to a fully open or fully closed state in accordance with predetermined operating conditions. It just controls whether or not to do. In addition, recently, an intake throttle valve is provided on the upstream side of the confluence portion of the exhaust gas recirculation passage in the intake passage. An exhaust gas recirculation control device which can be controlled stepwise has also been proposed (for example, "Service Weekly Report No. 578" B-1 issued by Nissan Motor Co., Ltd. in June 1987).
(See page 20).

[0003]

However, in the above-mentioned conventional exhaust gas recirculation control device, the open / closed state of the exhaust gas recirculation control valve and the opening degree of the intake throttle valve are uniquely determined according to the engine operating conditions such as the engine speed and the load. Since it is a configuration that is controlled dynamically,
It cannot escape the change in characteristics over time. For example,
When an exhaust particulate collection filter is installed in the exhaust system to collect exhaust particulates, which is a problem in diesel engines, the pressure loss increases with the collection of exhaust particulates, and the exhaust pressure increases. Although it will rise, when the exhaust pressure rises in this way, in the above conventional exhaust gas recirculation control device,
There is a problem that the amount of exhaust gas recirculation passing through the exhaust gas recirculation control valve increases, resulting in smoke, an increase in exhaust particulates, deterioration of HC, and the like.

Although it is possible to measure the exhaust gas flow rate from the pressure at an appropriate position in the exhaust gas recirculation passage, for example, the differential pressure between the upper and lower sides of the exhaust gas recirculation control valve, the detection accuracy decreases depending on the operating conditions. For example, when the exhaust gas recirculation control valve is almost fully opened, the pressure difference between the upper and lower sides of the valve becomes very small, so it is difficult to control the exhaust gas recirculation amount based on this.

[0005]

An exhaust gas recirculation control system for a diesel engine according to the present invention, as shown in FIG. 1, is an operating condition detecting means 1 for detecting an operating condition of a diesel engine.
And is installed in the exhaust gas recirculation passage from the exhaust system to the intake system,
An exhaust gas recirculation control valve 2 for controlling the exhaust gas recirculation amount, a first differential pressure detection means 3 for detecting a differential pressure ΔP1 upstream and downstream of an orifice provided between the exhaust gas recirculation control valve and the intake system, and the exhaust gas. A second differential pressure detecting means 4 for detecting a differential pressure ΔP2 upstream and downstream of the recirculation control valve 2, and a selecting means 5 for selecting which differential pressure is to be controlled based on engine operating conditions.
And a target value setting means 6 for setting a selected target value of the differential pressure according to the engine operating conditions, and the exhaust gas recirculation control so that the detected value of the selected differential pressure matches the target value of the differential pressure. The opening degree control means 7 which controls the opening degree of the valve 2 is provided, It is characterized by the above-mentioned.

According to the second aspect of the present invention, as shown in FIG. 2, the target value setting means 6 causes the differential pressure Δ to change in accordance with the operating conditions.
The reference differential pressure setting means 11 for setting the reference value of P2, the reference opening setting means 12 for setting the reference value of the opening degree of the exhaust gas recirculation control valve 2 in accordance with the operating conditions, and the current exhaust gas recirculation control valve 2 A second target value setting means 13 is provided which corrects the reference differential pressure by the control opening and the reference opening and sets a target value of the differential pressure ΔP2.

[0007]

When the flow coefficient of the orifice provided in the exhaust gas recirculation passage is A1, the exhaust gas recirculation amount Qe is expressed as Qe = A1√ (ΔP1) using the differential pressure ΔP1 between the upper and lower sides of the orifice. Therefore, if the opening degree of the exhaust gas recirculation control valve 2 is controlled so that the differential pressure ΔP1 becomes the differential pressure target value corresponding to the operating condition, the exhaust gas recirculation amount Qe itself is correctly maintained at the target value.

Similarly, since the exhaust gas recirculation control valve 2 can also be regarded as a kind of orifice, its flow coefficient is A
If it is 2, the exhaust gas recirculation amount Qe is shown as Qe = A2√ (ΔP2) using the differential pressure ΔP2 between the upper and lower sides of the exhaust gas recirculation control valve 2. Therefore, if the opening degree of the exhaust gas recirculation control valve 2 is controlled so that the differential pressure ΔP2 becomes the differential pressure target value corresponding to the operating condition, the exhaust gas recirculation amount Qe itself is correctly maintained at the target value.

Here, for example, in the low speed and low load region, a large amount of exhaust gas recirculation amount is required, so that the opening degree of the exhaust gas recirculation control valve 2 is close to full opening, and the differential pressure ΔP2 is small. On the other hand, the differential pressure ΔP1 across the orifice becomes large. In particular,
When performing intake throttle to secure a large amount of exhaust gas recirculation,
The differential pressure ΔP1 further develops. Therefore, by selecting the differential pressure ΔP1 as the control target by the selection means 5, the exhaust gas recirculation amount control can be accurately performed.

Further, in the medium-speed / medium-load region where the exhaust gas recirculation amount is small, the differential pressure ΔP1 across the orifice is small. On the other hand, since the opening degree of the exhaust gas recirculation control valve 2 becomes smaller,
The differential pressure ΔP2 above and below that develops. Therefore, the selection means 5
Thus, the exhaust gas recirculation amount control can be performed accurately by selecting the differential pressure ΔP2 as the control target.

On the other hand, the differential pressure ΔP2 above and below the exhaust gas recirculation control valve 2
When is selected as the control target, the flow rate coefficient A2 changes depending on the opening degree. This can be obtained as a known characteristic in advance, but in the invention of claim 2, the target value of the differential pressure ΔP2 is corrected so as to eliminate the influence such as the exhaust pressure increase due to the pressure loss in the exhaust system. . That is, when the reference differential pressure setting means 11 and the reference opening degree setting means 12 set respective reference values according to the operating conditions, and the current control opening degree of the exhaust gas recirculation control valve 2 is different from the reference opening degree, both By correcting the reference differential pressure using the value of the opening degree, the target value of the differential pressure ΔP2 is obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 3 is a structural explanatory view showing an embodiment of an exhaust gas recirculation control device according to the present invention, in which an intake passage 23 is connected to a combustion chamber 21 of a diesel engine via an intake valve 22. , Exhaust passage 25 through exhaust valve 24
Are connected. A butterfly valve type intake throttle valve 26 is provided in the intake passage 23. The intake throttle valve 26 is driven by an actuator (not shown), and can be controlled stepwise in three positions: a fully open position, a middle opening position, and a small opening position.

The exhaust gas recirculation passage 27 is formed from the exhaust passage 25 of the diesel engine to the intake passage 23, and a diaphragm type exhaust gas recirculation control valve 28 is interposed in the passage. The tip of the exhaust gas recirculation passage 27 is connected to the intake passage 23 downstream of the intake throttle valve 26.

In the negative pressure chamber 29 of the exhaust gas recirculation control valve 28, the vacuum pump 30 serving as a negative pressure source and the negative pressure passage 4 are provided.
Negative pressure is introduced through 0, and the opening degree of the exhaust gas recirculation control valve 28 is variably controlled by the duty ratio control of the duty control type solenoid valve 31 provided in the negative pressure passage 40. It has become. The above vacuum pump 30
Is driven by the output of a diesel engine together with a fuel injection pump (not shown).

An orifice 32 is provided at the tip of the exhaust gas recirculation passage 27, that is, at the junction with the intake passage 23. The pressure P2 on the upstream side of the orifice 32, that is, between the orifice 32 and the exhaust gas recirculation control valve 28,
A first differential pressure sensor 33 is provided so as to detect the differential pressure ΔP1 with the pressure Pi in the intake passage 23 on the downstream side, that is, on the downstream side of the intake throttle valve 26. Similarly, the second differential pressure sensor 34 is provided so as to detect the differential pressure ΔP2 between the upstream pressure Pe and the downstream pressure P2 of the exhaust gas recirculation control valve 28. The pressure of each part may be individually detected by the pressure sensor to calculate the differential pressure.

The detection signals of these differential pressure sensors 33, 34 are input to a control unit 35 using a microcomputer system. Further, 36 is a load sensor for detecting the load Q of the engine, for example, a control lever opening degree of the fuel injection pump, 37 is a rotation speed sensor for detecting the rotation speed Ne of the engine, and 38 is a cooling water temperature Tw of the engine. It is a water temperature sensor, and these detection signals are also input to the control unit 35. Then, according to the output signal of the control unit 35, the solenoid valve 3
1 and the intake throttle valve 26 are controlled.

Next, FIG. 4 is a flow chart showing the contents of the exhaust gas recirculation control in the above construction, and the operation of the above embodiment will be described below based on this flow chart.
The routine shown in this flowchart is repeatedly executed at regular intervals.

First, in step 1 (abbreviated as S1 etc. in the flowchart), the engine speed Ne of the diesel engine,
The load Q and the cooling water temperature Tw are read from the output signals of the respective sensors, and in step 2, the cooling water temperature Tw is the predetermined temperature Tw1.
It is determined whether or not the above. When the water temperature Tw has not reached Tw1, the exhaust gas recirculation is not performed and the duty ratio D is set to 0 (step 4). Similarly, in step 3, based on the rotation speed Ne and the load Q, it is determined whether or not the operation region is where the exhaust gas recirculation should be performed. If it is outside the exhaust gas recirculation region, the duty ratio D is also set to 0 in step 4.
And FIG. 5 shows the characteristics of the required exhaust gas recirculation rate with respect to the rotational speed Ne and the load Q. As is clear from this figure, the exhaust gas recirculation is stopped on the high speed and high load side, and at the low speed in the exhaust gas recirculation region. The required exhaust gas recirculation rate increases on the low load side.

If the condition is such that exhaust gas recirculation is to be performed, the routine proceeds to step 5, where the differential pressures ΔP1 and ΔP2 detected by the differential pressure sensors 33 and 34 are read. Further, in steps 6 and 7, the open / closed state of the intake throttle valve 26 is determined from the control map. FIG. 6 is a control map of the intake throttle valve 26. In the exhaust gas recirculation region, the intake throttle valve 26 is fully opened in the medium speed / medium load region where the required exhaust gas recirculation ratio is low, and conversely, when the required exhaust gas recirculation ratio is high. The opening is small on the low load side. And in the middle of both, it is controlled to the middle opening.

If it is determined in step 7 that the opening degree is medium or small, the process proceeds to step 8 and subsequent steps, and the orifice 32 is opened.
The control is performed by focusing on the upper and lower differential pressure ΔP1. That is, in this case, as shown in FIG. 6, it is in the low speed and low load region and the required exhaust gas recirculation rate is high. Therefore, the exhaust pressure is not so high and the exhaust gas recirculation control valve 28 is in a state of being almost fully opened, so that the differential pressure ΔP2 is small. On the other hand, the orifice 32
The upper and lower differential pressure ΔP1 is increased due to the large amount of exhaust gas recirculation, and the intake throttle valve 26 causes the pressure P in the intake passage 23 to rise.
It develops further because i decreases. FIG. 7 shows the differential pressure Δ
The relationship between P1 and the exhaust gas recirculation amount Qe is shown. In the region where the intake throttle valve 26 has a medium opening or a small opening, the differential pressure Δ
The value of P1 is large, and the change of the exhaust gas recirculation amount Qe with respect to the change of the differential pressure ΔP1 becomes gentle. Therefore, by performing feedback control of the opening degree of the exhaust gas recirculation control valve 28 using this differential pressure ΔP1, the exhaust gas recirculation amount Qe can be controlled with extremely high accuracy.

Specifically, in step 8, the target value ΔP1 _T of the differential pressure ΔP1 is set according to the operating conditions (rotational speed Ne and load Q) based on the control map shown in FIG. Then, in step 9, the detected differential pressure ΔP1 is compared with the differential pressure target value ΔP1 _T, and the actual differential pressure ΔP1 is calculated as the target value ΔP1.
If it is smaller than _T , the duty ratio D is increased (step 10), and if it is the target value ΔP1 _T or more, the duty ratio D is decreased (step 11). The control signal with the duty ratio D thus determined is output in step 12.

That is, the actual differential pressure ΔP1 is always the target value Δ
Feedback control is performed so as to coincide with P1 _T. As described above, the flow coefficient of the orifice 32 is set to A1.
Then, the exhaust gas recirculation amount Qe is Qe = A1√ (ΔP1)
Given as. Since the orifice 32 is a fixed orifice, the flow coefficient A1 has a fixed value.

On the other hand, when it is determined in step 7 that the intake throttle valve 26 is fully open, the process proceeds to step 13 and subsequent steps, and the control is performed by focusing on the differential pressure ΔP2 between the upper and lower exhaust gas recirculation control valves 28. That is, in this case, as shown in FIG. 6, it is in the medium speed / medium load region, and the required exhaust gas recirculation rate is relatively low. Therefore, the exhaust pressure becomes relatively high, the opening degree of the exhaust gas recirculation control valve 28 becomes small, and the differential pressure ΔP2 above and below the exhaust gas recirculation control valve 28 develops. On the other hand, the differential pressure ΔP1 across the orifice 32 is
Since the exhaust gas recirculation amount is small, the exhaust gas recirculation amount is small. Further, since the intake throttle valve 26 is fully opened and the pressure Pi in the intake passage 23 is substantially atmospheric pressure, the development thereof is further suppressed. Therefore, in this case, highly accurate feedback control can be realized by using the differential pressure ΔP2 between the upper and lower sides of the exhaust gas recirculation control valve 28.

Specifically, in step 13, the reference value of the differential pressure ΔP2 corresponding to the operating condition at that time, that is, the reference differential pressure ΔP2 _S is set based on the control map shown in FIG. In step 14, the reference value of the duty ratio D corresponding to the operating condition at that time, that is, the reference duty ratio D
_S is set based on the control map shown in FIG. These reference values are standard values on the assumption that there is no increase in pressure loss in the exhaust filter. Next, in steps 15 and 16, the actually detected differential pressure ΔP2 is compared with its target value ΔP2 _T. The target value ΔP2 _T of the differential pressure ΔP2 is obtained in step 1 described later.
The value calculated in 9 is used. If there is no increase in pressure loss in the exhaust filter, the target value ΔP2 _T is equal to the reference differential pressure ΔP2 _S.

When the actual differential pressure ΔP2 is smaller than the target value ΔP2 _T , the duty ratio D is increased (step 1
7) On the other hand, if it is larger than the target value ΔP2 _T , the duty ratio D is decreased (step 18). The control signal for which the duty ratio D is determined in this way is also output in step 12. That is, feedback control is always performed so that the actual differential pressure ΔP2 matches the target value ΔP2 _T.

When it is determined in step 15 that the actual differential pressure ΔP2 and the target value P2 _T coincide with each other, step 1
9, the target value ΔP2 _T is calculated using the duty ratio D, the reference duty ratio D _S, and the reference differential pressure ΔP2 _{S at} that time.
To calculate. Specifically, ΔP2 _T = (D _S / D) ² · Δ
Calculate as P2 _S.

That is, if the exhaust gas recirculation control valve 28 is regarded as a kind of orifice, its flow coefficient is represented by A2, and the exhaust gas recirculation amount Qe is expressed by Qe = A2√ (ΔP2). The coefficient A2 is not a fixed value but changes depending on the opening degree of the exhaust gas recirculation control valve 28, as shown in FIG. However, in the region where the exhaust gas recirculation amount Qe in which the differential pressure ΔP2 is controlled is small, it can be approximated by a straight line having a relatively small inclination as shown by the broken line in FIG. Also,
In the above configuration in which a stable negative pressure is supplied by the vacuum pump 30, the lift amount of the exhaust gas recirculation control valve 28 and the duty ratio D of the drive signal are in a proportional relationship. Therefore, within the linearly approximated range, the relationship of A2 = C · D is established for the flow coefficient A2, where C is the proportional constant.

Using this relationship, the target exhaust gas recirculation amount Qe is Qe = A2√ (ΔP2 _S ) = C · D _S √ (Δ, using the reference duty ratio D _S and the reference differential pressure ΔP2 _S.
P2 _S ).

Here, when the exhaust pressure changes due to clogging of the exhaust filter or the like, a constant differential pressure ΔP2 (target value ΔP2
The actual duty ratio D when feedback control is performed to _T ) changes. Then, since the flow rate coefficient A2 changes as it is, an error occurs in the exhaust gas recirculation amount Qe.

In order to secure the predetermined exhaust gas recirculation amount Qe regardless of the change of the duty ratio D, a new target value Δ
As P2 _T , Qe = C · D _S √ (ΔP2 _S ) = C · D
Since the relationship of √ (ΔP2 _T ) needs to be established, from this expression, conversely, the required target value ΔP2 _T is ΔP2 _T =
It is calculated as (D _S / D) ² · ΔP2 _S. Therefore,
Thus, by successively calculating the target value ΔP2 _T in step 19, the exhaust gas recirculation amount Qe can be accurately controlled to a desired value even when the exhaust pressure changes.

In the above-mentioned region in which the pressure difference ΔP1 between the upper and lower sides of the orifice 32 is controlled, since the orifice 32 is a fixed orifice, it is not affected by the exhaust pressure change.

Thus, according to the above embodiment, the differential pressure ΔP
Since the feedback control for 1 and the feedback control for the differential pressure ΔP2 are switched and executed depending on the operating conditions, the exhaust gas recirculation amount Qe can be controlled with high accuracy under a wide range of operating conditions. Moreover, even if the exhaust pressure rises due to clogging of the exhaust filter or the intake pressure changes due to clogging of the air cleaner element, the desired exhaust gas recirculation amount Qe is maintained without being affected by this. can do.

In the above embodiment, the differential pressure ΔP1 and the differential pressure Δ
Although the control switching between P2 and P2 is made to coincide with the opening switching point of the intake throttle valve 26, the present invention is not limited to this.

Next, FIG. 12 shows an embodiment in which the exhaust gas recirculation control valve 28 is provided with a lift sensor 39 for detecting the lift amount L thereof. According to this embodiment, the flow rate coefficient A2 can be obtained more accurately from the characteristics shown in FIG. 9, and the correction for the exhaust pressure and the like in the feedback control using the differential pressure ΔP2 becomes even more accurate. In this case, the reference lift amount L _S is given by a predetermined control map instead of the reference duty ratio D _S of the above-described embodiment. Also, ΔP
The target value ΔP2 _{T of} 2 is ΔP2 _T = (L _S / L) ² · Δ
It is sequentially calculated as P2 _S.

[0036]

As is apparent from the above description, according to the exhaust gas recirculation control device for a diesel engine of the present invention, the vertical differential pressure ΔP2 of the exhaust gas recirculation control valve or the vertical differential pressure of the orifice provided downstream thereof. Since the opening degree of the exhaust gas recirculation control valve is feedback-controlled by any of ΔP1, the exhaust gas recirculation amount can be finely controlled. In particular, the most suitable one is selected as the control target according to the operating conditions, and feedback control is performed so that the differential pressure is maintained at the target value, so highly accurate exhaust gas recirculation amount control is achieved under a wide range of operating conditions. it can.

Further, if the target value of the differential pressure ΔP2 is corrected by the reference opening and the actual control opening as in claim 2, for example, the pressure loss of the exhaust filter increases and the air cleaner element becomes clogged. Can be eliminated, and the excess and deficiency of the excluded reflux amount will not occur. That is, it is possible to prevent the characteristics from changing with time, and to prevent the smoke from being deteriorated due to the increase in the exhaust gas recirculation amount.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of an exhaust gas recirculation control device according to the present invention.

FIG. 2 is a claim correspondence diagram showing the configuration of the invention of claim 2;

FIG. 3 is a structural explanatory view showing a mechanical structure of an embodiment of the present invention.

FIG. 4 is a flowchart showing the contents of exhaust gas recirculation control in this embodiment.

FIG. 5 is a characteristic diagram showing characteristics of exhaust gas recirculation rate with respect to operating conditions.

FIG. 6 is a characteristic diagram showing an opening characteristic of an intake throttle valve with respect to operating conditions.

FIG. 7 is a characteristic diagram showing a relationship between a differential pressure ΔP1 and an exhaust gas recirculation amount.

FIG. 8 is a characteristic diagram showing characteristics of a target value of the differential pressure ΔP1 with respect to operating conditions.

FIG. 9 is a lift amount of the exhaust gas recirculation control valve and its flow coefficient A2.
The characteristic view showing the relationship with.

FIG. 10 is a characteristic diagram showing characteristics of a reference differential pressure ΔP2 _S with respect to operating conditions.

FIG. 11 is a characteristic diagram showing characteristics of a reference duty ratio D _{S with} respect to operating conditions.

FIG. 12 is a structural explanatory view showing an embodiment in which a lift sensor is provided.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Operating condition detection means 2 ... Exhaust gas recirculation control valve 3 ... 1st differential pressure detection means 4 ... 2nd differential pressure detection means 5 ... Selection means 6 ... Target value setting means 7 ... Opening degree control means 11 ... Reference differential pressure setting Means 12 ... Reference opening setting means 13 ... Second target value setting means

Claims (2)

[Claims] 1. An operating condition detecting means for detecting an operating condition of a diesel engine, an exhaust gas recirculation control valve for controlling an exhaust gas recirculation amount, which is interposed in an exhaust gas recirculation passage extending from an exhaust system to an intake system, and the exhaust gas recirculation control. A first differential pressure detecting means for detecting a differential pressure ΔP1 upstream and downstream of an orifice provided between the valve and the intake system, and a second differential pressure detecting a differential pressure ΔP2 upstream and downstream of the exhaust gas recirculation control valve. A detection means, a selection means for selecting which of the differential pressures to perform control based on the engine operating conditions, and a target value setting means for setting a target value of the selected differential pressure according to the engine operating conditions, An exhaust gas recirculation system for a diesel engine, comprising: an opening degree control means for controlling the opening degree of the exhaust gas recirculation control valve so that the detected value of the selected differential pressure matches the differential pressure target value. Control device. 2. The target value setting means sets a reference differential pressure setting means for setting a reference value of the differential pressure ΔP2 according to operating conditions, and a reference value of the opening degree of the exhaust gas recirculation control valve according to operating conditions. And a second target value setting means that corrects the reference differential pressure by the current control opening of the exhaust gas recirculation control valve and the reference opening, and sets a target value of the differential pressure ΔP2. The exhaust gas recirculation control device for a diesel engine according to claim 1, further comprising: