JP3250322B2 - EGR control device for diesel engine - Google Patents

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 control device.

[0002]

2. Description of the Related Art 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.

[0003] The required value of the recirculation amount of exhaust gas (EGR flow rate) differs depending on the operating conditions.
Since R impairs the output performance of the engine, a target value of the EGR rate (= EGR flow rate / intake air flow rate) according to the operating conditions is determined in advance so that the engine output performance and the exhaust performance are balanced. And the target EGR that matches the current operating condition by referring to the map of the target value.
The opening ratio of the EGR valve and the intake throttle valve is controlled by calculating the target EGR ratio, converting the target EGR ratio into a control command value, and supplying this to each actuator for 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 the adhesion of carbon contained in the EGR gas to the EGR valve, Exhaust performance may deteriorate.

[0005] For this reason, in Japanese Patent Application Laid-Open No. 57-165656, the actual EGR rate is detected at every fixed traveling distance.
The feedback control of the control command value to the EGR valve actuator is performed so that this coincides with the target value. A sensor for detecting the intake air flow rate and the EGR flow rate is provided, and the actual EGR rate is obtained from the sensor detection values. If the actual EGR rate is larger than the target value, the EGR valve opening degree becomes smaller, and vice versa. 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]

In the above-described apparatus, the passage is branched into two in the middle of the EGR passage to detect the EGR flow rate, and one of the branch passages is provided with a venturi portion. The differential pressure is taken out by a differential pressure transducer. Since the flow rate in the venturi section is determined from the flow path area of the venturi section and the pressure difference between the front and rear, the differential pressure is converted into the EGR flow rate using this relationship.

However, under operating conditions such as a low rotation region and a low EGR flow region, the differential pressure across the venturi becomes small, and the EGR flow cannot be accurately detected.
When the feedback control of the EGR rate is performed using the inaccurate detected value of the EGR flow rate, the feedback control accuracy is rather reduced.

Accordingly, the present invention reduces the flow passage area of the variable orifice provided in the EGR passage in a low rotation region while performing feedback control with a target value of a pressure difference between the exhaust passage and the intake passage downstream of the intake throttle valve. Accordingly, it is an object to prevent the setting accuracy of the EGR rate in a low rotation speed range from being deteriorated.

[0009]

According to the present invention, as shown in FIG. 1, an EGR for communicating an exhaust passage 31 and an intake passage 32 is provided.
A passage 33 and an EGR valve 3 for opening and closing the EGR passage 33
4, an actuator (for example, a duty control valve) 35 capable of variably adjusting the opening degree of the EGR valve 34, a valve 36 located upstream of the connection between the EGR passage 33 and the intake passage 32, and restricting intake air. An actuator 37 that can adjust the opening degree of the intake throttle valve 36 in multiple stages and a detected value of an operating condition (for example, the engine speed Ne and the engine load L
means 38 for controlling the intake throttle valve actuator 37 so as to obtain an intake throttle valve opening corresponding to p);
An orifice 39 for variably adjusting the flow passage area of the GR passage 33;
Means 41 for reducing the flow path area of the variable orifice 39 when it is determined that it is a predetermined low rotation range,
The target value ΔPt of the differential pressure between the exhaust passage 31 and the intake passage 33 downstream of the intake throttle valve 36 according to the detected value of the operating condition.
Between the predetermined rotation range and the other rotation ranges, and in accordance with the orifice flow path area which is reduced in the predetermined rotation range and the orifice flow path area which is not reduced in the other rotation ranges. 42, a sensor 43 for actually measuring the differential pressure between the exhaust passage 31 and the intake passage 33 downstream of the intake throttle valve 36, and the actual measured differential pressure value ΔPs and the target differential pressure value ΔPt match. Thus, the means 43 for feedback-controlling the control command value to the EGR valve actuator 35 is provided.

[0010]

The measured value of the EGR differential pressure increases due to the decrease in the flow path area of the variable orifice in a predetermined low rotation range, so that the measurement accuracy of the measured value increases, and the feedback control to the target EGR rate is performed at a low rotation speed. It is performed with high accuracy even in the area.

If feedback control is performed using the EGR differential pressure as a target value instead of the EGR rate as a direct target value, the particulate matter accumulates in a post-processing device provided in the exhaust passage and the exhaust pressure increases. However, a target EGR rate corresponding to the operating conditions can be obtained.

[0012]

In FIG. 2, an EGR passage 3 communicating the exhaust passage 1 and the intake passage 2 is provided with an EGR valve 5 for opening and closing the EGR passage 3 near a connection with the exhaust passage 1.

The EGR valve 5 has a valve lift (a value corresponding to a valve opening) which is adjusted by a duty control valve (actuator) 6 to adjust a duty ratio (an ON time ratio per fixed time period) given to the control valve 6. The valve lift increases in proportion. As the duty ratio increases, the vacuum pump (driven by the engine) becomes higher than the atmospheric pressure.
The rate of introduction of the constant negative pressure from the valve increases, the control negative pressure of the EGR valve to the working chamber 5A 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, 20 degrees). (30 degrees, 80 degrees). EGR
Even if the lift of the valve 5 is the same, the greater the differential pressure across the
Since the GR flow rate increases, the control negative pressure applied to the diaphragm actuator 10 is increased to close the intake throttle valve 8, and E
The differential pressure across the GR valve 5 increases, and the EGR flow increases.

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

FIG. 3 shows the characteristics when the exhaust system is not provided with a flow path resistance. When the exhaust passage 1 is provided with a post-processing device such as a filter for collecting particulates, In the same operating conditions, the exhaust pressure increases as the amount of trapped particulates in the exhaust after-treatment device increases, so that the EGR flow increases with the increase in the exhaust pressure, and the actual EGR rate becomes higher than the target value. It will come off.

As a measure against this exhaust, pressure sensors (absolute pressure sensors) 1 provided in the EGR passage 3 and the intake passage 2 respectively.
At 3 and 14, the pressure difference between the two passage pressures is measured (this pressure difference is referred to as the EGR pressure difference). In the control unit 11 composed of a microcomputer, the measured value of the EGR pressure difference is the value of the EGR pressure difference determined according to the operating conditions. If the duty ratio given to the control valve 6 is corrected so as to match the target value, the EGR rate can be kept constant even when the exhaust pressure increases. FIG. 4 shows the effect of increasing the exhaust pressure above the standard exhaust pressure (5 mmHg in the figure, in the absence of a post-treatment device, under the same operating conditions). The reason 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. Instead of the two pressure sensors 13 and 14, a differential pressure sensor that directly detects the differential pressure between the two passage pressures may be used.

However, since the gradient of the EGR differential pressure with respect to the EGR rate becomes smaller as the rotation speed becomes lower as shown in FIG. 5, it is impossible to accurately detect the actual EGR differential pressure in the low rotation speed region. Even if the EGR rate changes in the low rotation range, the measured value of the EGR differential pressure does not change before and after the change in the EGR rate.

Therefore, in this example, as shown in FIG.
A normally open variable orifice 15 is provided at the connection between the GR passage 3 and the intake passage 2, and the control unit 11 performs feedback control with the EGR differential pressure as a target value according to the positions shown in FIGS. By closing the variable orifice 15 to the half-open position in the low rotation range, an EGR differential pressure required in the low rotation range is created.

The variable orifice 15 can be constituted by a butterfly valve.

FIG. 6 is a flowchart for controlling the duty ratio given to the control valve 9 for the intake throttle valve, and FIG. 8 is a flowchart for controlling the duty ratio given to the control valve 6 for the EGR valve and the variable orifice 15, respectively.

<1> Control of the intake throttle valve As shown in FIG. 6, by referring to the map containing the opening degree characteristics of the intake throttle valve in FIG. 3 based on the engine speed Ne and the engine load Lp, The throttle valve opening in the region to which the operating condition belongs is obtained, converted into a duty ratio using a table having the contents shown in FIG. 7, and output to the control valve 9 as a duty signal (FIG. 6). Step 1
4) The intake throttle valve 8 is controlled in three stages.

<2> Feedback control using EGR differential pressure as target value The target EGR rate is determined by the engine speed Ne and the engine load L
From p, a map containing the characteristics of the target EGR rate in FIG. 3 may be referred to (step 12 in FIG. 8), and a map containing contents in FIG. Thus, a target value ΔPt of the EGR differential pressure is obtained (step 13 in FIG. 8).

The target value ΔPt of the EGR differential pressure basically increases as the target EGR rate increases.
If the rate is the same, it becomes smaller as the rotation becomes lower,
As shown in FIG. 9, a predetermined number of rotations (for example, 1200
(rpm) or lower, the characteristics are different from those of the rotation range exceeding 1200 rpm. As described later, the variable orifice 1 is used in a low rotation range of 1200 rpm or less.
This is because when the valve 5 is closed to the half-open position, the actual measured value of the EGR differential pressure becomes larger than when the variable orifice 15 is at the fully-open position, and accordingly, the target value ΔPt must be increased accordingly. In other words, the characteristic of the target value ΔPt of the EGR differential pressure shown in FIG.
In the rotation range exceeding 200 rpm, the value is in accordance with the area of the orifice passage at the fully open position.

The target value ΔPt of the EGR differential pressure thus determined
The lift target value Ht of the EGR valve is obtained with reference to the map containing the contents of FIG. 10 from the engine speed Ne and the engine speed Ne, and this is converted into the duty ratio Dt to the control valve 6 using the table containing the contents of FIG. (Steps 14 and 1 in FIG. 8)
5).

On the other hand, looking at the value of the rotation speed Ne,
If it is 0 rpm or less, it is determined that the engine is in the low rotation range, and O is set so that the variable orifice 15 is closed to the half open position.
An N signal is output (steps 16 and 17 in FIG. 8).

From the signals of the two pressure sensors 13 and 14, E
The measured value ΔPs of the GR differential pressure is read and compared with the target value ΔPt of the EGR differential pressure. If ΔPt ≠ ΔPs, the duty ratio Dt to the control valve 6 is adjusted so that the measured value ΔPs matches the target value ΔPt. Is corrected. If ΔPt <ΔPs, the value obtained by subtracting the constant value ΔDt from the duty ratio Dt is newly set as the duty ratio Dt, thereby obtaining the EGR.
Correct the valve 5 to the closing side (steps 20, 21, and 20 in FIG. 8).
23) Conversely, when ΔPt> ΔPs, the duty ratio Dt is corrected to increase and the EGR valve 5 is driven to the open side (steps 20, 22, and 23 in FIG. 8).

As described above, the variable orifice 1
By closing 5 to the half-open position, the measured value of the EGR differential pressure increases, so that the measurement accuracy of the measured value increases, and the feedback control to the target EGR rate can be performed with high accuracy even in a low rotation range.

In addition, by performing feedback control using the EGR differential pressure as a target value instead of setting the EGR rate directly as a target value, when particulates accumulate in a post-processing device provided in an exhaust passage and the exhaust pressure increases. However, a target EGR rate corresponding to the operating conditions can be obtained. When the EGR rate is set to the direct target value, the exhaust pressure rises even under the same operating conditions,
The EGR flow increases (the EGR rate changes).

FIG. 12 shows another embodiment. This is EG
A variable orifice is composed of passages 21 and 22 that branch a connection portion of the R passage 3 with the intake passage 2 into two, and a normally open shutter valve 23 provided in one branch passage 21.
The shutter valve 23 is fully closed in a low rotation range.

According to this embodiment, since the flow of the EGR gas can be more reliably prevented as compared with the above-mentioned embodiment constituted by the butterfly valve, the effect of increasing the EGR differential pressure is higher than that of the first embodiment. growing.

The orifices 24 and 25 are provided in the two branch passages 21 and 22, respectively, because the EGR differential pressure cannot be secured when only the shutter valve 23 is opened.

In the embodiment, the intake throttle valve 8 is set at 20 degrees and 30 degrees.
And the rotation speed at which the characteristic of the target value ΔPt of the EGR differential pressure is changed to 1200 rpm. However, the actual throttle valve opening value such as 20 degrees, 30 degrees, and 80 degrees is used. As for a value such as 1200 rpm, it goes without saying that an appropriate value differs depending on the engine model and the throttle valve specification.

[0034]

According to the present invention, an orifice capable of variably adjusting the flow path area of the EGR passage is provided, and when it is determined that the engine is in a predetermined low rotation range, the flow area of the variable orifice is reduced. On the other hand, according to the detected value of the operating condition, the target value of the differential pressure between the exhaust passage and the intake passage downstream of the intake throttle valve is made different between the predetermined rotation region and the other rotation regions, and the predetermined rotation region is changed. The EGR is calculated in accordance with the orifice flow path area to be reduced and the orifice flow path area which is not reduced in the other rotation ranges, and the EGR is set so that the target differential pressure value and the measured differential pressure value match. Since the control command value to the valve actuator is configured to be feedback-controlled, the feedback control to the target EGR rate can be performed with high accuracy even in a low rotation range, and the post-processing provided in the exhaust passage can be performed. Device even when particulates accumulate discharge pressure increases, the target E in accordance with the operating conditions
A GR rate is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present 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 shows the relationship between the EGR rate when the exhaust pressure is increased and the NO.
It is each characteristic figure of x discharge amount, EGR differential pressure, intake air flow rate, and EGR valve lift.

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

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

FIG. 7 is a characteristic diagram of a duty ratio with respect to a throttle valve opening target value.

FIG. 8 is a flowchart showing control contents of a control unit 11;

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

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

FIG. 11 is a characteristic diagram of a duty ratio with respect to a lift target value Ht of the EGR valve.

FIG. 12 is a schematic view of a variable orifice according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 1 exhaust passage 2 intake passage 3 EGR passage 5 EGR valve 6 duty control valve (actuator for EGR valve) 8 intake throttle valve 9 duty control valve (actuator for intake throttle valve) 11 control unit 13, 14 pressure sensor 15 variable orifice 21, Reference Signs List 22 branch passage 23 shutter valve 31 exhaust passage 32 intake passage 33 EGR passage 34 EGR valve 35 EGR valve actuator 36 intake throttle valve 37 intake throttle valve actuator 38 throttle valve control means 39 variable orifice 40 low rotation range determination means 41 flow path Area reducing means 42 Differential pressure target value calculating means 43 Differential pressure sensor 44 Feedback control means

Continuation of the front page (56) References JP-A-57-70944 (JP, A) JP-A-5-18323 (JP, A) JP-A-6-294355 (JP, A) JP-A-2-267360 (JP) JP-A-4-272460 (JP, A) JP-A-6-307292 (JP, A) JP-A-59-160845 (JP, U) JP-A-63-198458 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02M 25/07 570 F02M 25/07 550 F02D 21/08

Claims (1)

(57) [Claims] An EGR passage that communicates between an exhaust passage and an intake passage; an EGR valve that opens and closes the EGR passage;
An actuator capable of variably adjusting the opening of the R valve, a valve positioned upstream of the connection between the EGR passage and the intake passage to restrict intake air, and an actuator capable of adjusting the opening of the intake throttle valve in multiple stages Means for controlling the intake throttle valve actuator so as to obtain an opening degree of the intake throttle valve in accordance with the detected value of the operating condition; an orifice capable of variably adjusting the flow area of the EGR passage; Means for determining whether or not the engine is in a rotation range; means for reducing the flow area of the variable orifice when it is determined that the engine is in a predetermined low rotation range; The target value of the differential pressure between the intake passage downstream of the throttle valve and the predetermined rotation range is made different between the predetermined rotation range and the other rotation ranges, and in the predetermined rotation range, in accordance with the reduced orifice flow area,
In addition, a means for calculating each in accordance with the orifice passage area which is not reduced in the other rotation ranges, a sensor for measuring a pressure difference between the exhaust passage and the intake passage downstream of the intake throttle valve, Means for feedback-controlling a control command value to the EGR valve actuator so that the differential pressure target value coincides with the target value.