JP2000130265A - Egr device and engine controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the recirculation of EGR gas having the sufficient flow rate by increasing the pressure differential before and after an EGR valve in the low load of an engine. SOLUTION: In a turbocharger 11, an exhaust turbine 13 and an intake compressor 12 are coaxially connected to each other. In this case, a primary EGR passage 31 for making the upstream side of the exhaust turbine 13 communicate with the downstream side of a throttle valve 7 and a secondary EGR passage 32 for making the downstream side of the exhaust turbine 13 communicate with the upstream side of the intake compressor 12 are provided, and these two EGR passages 31, 32 are selectively used according to the operating conditions of an engine. The secondary EGR passage 32 is shut off in a low loading of the engine, and the primary EGR passage 31 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR device and an engine control device, and more particularly to a device having a turbocharger.

[0002]

2. Description of the Related Art E of an engine having a turbocharger
As a GR device, there is one in which an EGR valve is provided in an EGR passage that communicates the downstream of an exhaust turbine and the upstream of an intake compressor (Japanese Utility Model Laid-Open No. 2-43450, Japanese Utility Model Application Laid-Open No. 2-43450).
No. 46058).

[0003]

SUMMARY OF THE INVENTION However,
In the conventional device, when the engine is under a low load in which the intake air amount is small and the exhaust pressure does not increase, the differential pressure between the exhaust pressure on the downstream side of the exhaust turbine and the intake pressure on the upstream of the intake compressor is small, so that a sufficient flow of EGR gas cannot be recirculated. , N in exhaust
The effect of reducing Ox is not sufficient.

On the other hand, if the EGR valve is simply provided in the EGR passage communicating the upstream of the exhaust turbine and the downstream of the throttle valve, the downstream pressure of the throttle valve may become higher than the exhaust pressure upstream of the exhaust turbine due to supercharging. There is a backflow at this time, and EGR cannot be performed.

Accordingly, the present invention provides two EGR passages: a primary EGR passage communicating upstream of the exhaust turbine and downstream of the throttle valve, and a secondary EGR passage communicating downstream of the exhaust turbine and upstream of the intake compressor. The two EGR passages are selectively used according to the engine operating conditions. In this case, when the engine is under low load, the secondary EGR passage is shut off and the primary EG
By performing the EGR using the R passage, the differential pressure across the EGR valve is increased even at a low engine load to allow a sufficient flow of the EGR gas to be recirculated, and the downstream pressure of the throttle valve is increased upstream of the exhaust turbine. A first object is to shut off the primary EGR passage when the pressure becomes higher than the exhaust pressure and perform EGR using the secondary EGR passage so that EGR can be performed even when the supercharging pressure is increased.

[0006] In some cases, two EGR passages are provided to communicate the exhaust passage upstream and downstream of the positive displacement supercharger, respectively, and these two EGR passages are selectively used according to the operating conditions of the engine. 1-78234
This publication does not disclose a turbocharger.

On the other hand, a device capable of controlling the opening of the throttle valve independently of the accelerator pedal is provided, and by simultaneously controlling the opening of the throttle valve and the amount of fuel supplied to the engine, it is possible to operate at a lean air-fuel ratio. Known engines are known. When the EGR device of the present invention is combined with such an engine, the opening area of the throttle valve is calculated in order to flow the fresh air flow required from the engine torque and the air-fuel ratio, and the EG required to reduce NOx is calculated.
In order to achieve the R rate, the opening area of the EGR valve must be calculated.

However, when the throttle valve opening area and the EGR valve opening area are independently calculated, fresh air (air sucked through an air cleaner. EGR gas is not included.) ), The phases of the flow rate of the fresh air sucked into each cylinder and the flow rate of the EGR gas do not match. NOx
For reduction, a target EGR rate according to the operating conditions of the engine is predetermined, but if the flow rate of the fresh air and the flow rate of the EGR gas are out of phase, the actual EGR rate may deviate significantly from the target value. This leads to an increase in NOx during a transition and a significant loss of combustion stability of the engine.

Therefore, the present invention provides a method for determining the target flow rate of each of the primary and secondary EGR valves based on a target fresh air flow rate based on an accelerator operation amount and an engine speed and a target EGR rate corresponding to an engine operating condition. Calculate, calculate the total gas flow supplied to the engine based on the target flow rate and the target fresh air flow rate, calculate the total opening area corresponding to the total gas flow rate, and calculate the total opening area as the target of the throttle valve. By accurately distributing the opening area and the target opening areas of the two EGR valves, it is possible to accurately achieve both the fresh air flow rate required from the engine torque and the air-fuel ratio and the EGR rate required for NOx reduction. As a second object.

[0010] The above-mentioned conventional apparatus in which EGR is performed independently of the device for controlling the intake air amount does not disclose the point that the total opening area is obtained and distributed.

[0011]

According to a first aspect of the present invention, there is provided a turbocharger in which an exhaust turbine and an intake compressor are coaxially connected, a primary EGR passage communicating an upstream of the exhaust turbine with a throttle valve downstream, and a downstream of the exhaust turbine. A secondary EGR passage that communicates upstream of the intake compressor and these two EGR passages are selectively used according to the operating conditions of the engine.
Means for shutting off the GR passage and using the primary EGR passage.

According to a second aspect of the present invention, there is provided a turbocharger in which an exhaust turbine and an intake compressor are coaxially connected, a primary EGR passage communicating an upstream of the exhaust turbine and a throttle valve downstream, and a communication between a downstream of the exhaust turbine and an upstream of the intake compressor. The secondary EGR passage and these two EGR passages are selectively used according to the operating conditions of the engine,
Means are provided for shutting off the primary EGR passage and using the secondary EGR passage when the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine.

According to a third aspect of the present invention, there is provided a turbocharger in which an exhaust turbine and an intake compressor are connected coaxially, a primary EGR passage communicating between an upstream of the exhaust turbine and a throttle valve downstream, and a communication between a downstream of the exhaust turbine and an upstream of the intake compressor. The secondary EGR passage and these two EGR passages are selectively used according to the operating conditions of the engine,
Means for shutting off the secondary EGR passage and using the primary EGR passage when the engine load is low, and for shutting off the primary EGR passage and using the secondary EGR passage when the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine. Was.

According to a fourth aspect of the present invention, there is provided an engine provided with a turbocharger in which an exhaust turbine and an intake compressor are coaxially connected, as shown in FIG. 14, with a device 41 capable of controlling the opening of a throttle valve independently of an accelerator pedal. ,
EG that communicates upstream of the exhaust turbine and downstream of the throttle valve
A primary EGR valve 42 for opening and closing the R passage, and a device 43 capable of controlling the opening degree of the primary EGR valve 42
And a secondary EGR valve 44 for opening and closing an EGR passage communicating the downstream of the exhaust turbine and the upstream of the intake compressor.
A device 45 capable of controlling the degree of opening of the secondary EGR valve 44; a unit 46 for calculating a target fresh air flow rate based on an accelerator operation amount; and a unit 47 for calculating a target EGR rate in accordance with operating conditions of the engine. Means 48, 49 for calculating the respective target flow rates of the two EGR valves 42, 44 from the target fresh air flow rate and the target EGR rate;
Means 50 for calculating the total gas flow supplied to the engine based on the target flow of the R valves 42 and 44 and the target fresh air flow
Means 51 for calculating a total opening area corresponding to the total gas flow rate; means 52 and 53 for calculating target opening areas of the throttle valve and the two EGR valves 42 and 44 based on the total opening area. , 54 and the throttle valve control device 41 so as to have the target opening area of the throttle valve.
55, a means 56 for driving the primary EGR valve control device 43 so that the target opening area of the primary EGR valve 42 becomes the target opening area, and a means 56 for driving the secondary EGR valve.
Means 57 for driving the secondary EGR valve control device 45 so that the target opening area of the R valve 44 becomes the target opening area is provided.

According to a fifth aspect, in the fourth aspect, means 48, 49 for calculating the respective target flow rates of the two EGR valves.
Means for calculating a total EGR flow rate based on the target fresh air flow rate and the target EGR rate, means for calculating a differential pressure across the primary EGR valve, and a maximum flow rate of the primary EGR valve based on the differential pressure. When the total EGR flow rate exceeds the maximum flow rate of the primary EGR valve, the maximum flow rate of the primary EGR valve is set as the target flow rate of the primary EGR valve, and the maximum flow rate of the primary EGR valve is calculated from the total EGR flow rate. The remainder after subtraction is set as the target flow rate of the secondary EGR valve, and
When the total EGR flow rate is equal to or less than the maximum flow rate of the primary EGR valve, means for setting the total EGR flow rate as the target flow rate of the primary EGR valve and setting the target flow rate of the secondary EGR valve to zero.

According to a sixth aspect of the present invention, in the fourth or fifth aspect, the means for calculating the total gas flow rate converts each target flow rate of the primary EGR valve and the secondary EGR valve to a new air flow rate based on physical properties of the exhaust gas. Means for calculating the total of the two new air flow rate conversion values and the target fresh air flow rate as the total gas flow rate.

According to a seventh aspect, in the sixth aspect, the target fresh air flow rate relative to the total gas flow rate, the primary EGR
The target opening area of the throttle valve and the primary EGR valve are multiplied by three ratios of a new air flow conversion value of the target flow rate of the valve and a new air flow rate conversion value of the target flow rate of the secondary EGR valve. The target opening area and the target opening area of the secondary EGR valve are calculated.

[0018]

According to the first and third aspects of the present invention, the primary E having a large differential pressure across the EGR valve at a low engine load is used.
Since the GR passage is used, a sufficient flow of EGR gas can be recirculated even when the engine is under a low load.

According to the second and third aspects of the present invention, even when the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine, EGR can be performed through the secondary EGR passage.

According to the fourth aspect of the present invention, the total opening area from which the target fresh air flow rate and the target EGR rate can be obtained is first obtained, and this is distributed to the target opening area of the throttle valve and each target opening area of the two EGR valves. Therefore, fresh air flow required from engine torque and air-fuel ratio and EGR required to reduce NOx
Both the rate and the rate can be realized with high accuracy, whereby both the drivability of the vehicle and the reduction of NOx can be satisfied.

According to the fifth aspect of the present invention, in a region where the total EGR flow rate is small at a low engine load, the primary EGR valve having a large differential pressure across the EGR valve is used, so that a sufficient flow rate of the EGR gas is recirculated. be able to. In addition, when the supercharging pressure increases and the differential pressure across the EGR valve decreases, and the total EGR flow cannot be flowed using only the primary EGR valve, the supercharging pressure increases because the EGR is performed using the secondary EGR valve. In this state, the total EGR flow rate can be flowed without excess or shortage.

If the physical property values (pressure, temperature) of the EGR gas (that is, the exhaust gas) differ depending on the operating conditions of the engine, the EGR flow rate (mass flow rate) differs even with the same EGR valve opening area. Therefore, if the total gas flow rate is determined without performing physical property adjustment of the EGR gas and fresh air, the calculation accuracy of the total gas flow rate is reduced. Since the physical properties of the fresh air are adjusted, the calculation accuracy of the total gas flow rate does not decrease even if the operating conditions of the engine are different.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, 1 is an engine body, 2 is an intake passage, 3 is an exhaust passage, 4 is a fuel injection valve provided directly facing a combustion chamber 5, 6 is a spark plug, and 7 is a throttle. Valves 8 are throttle valve control devices for electronically controlling the opening of the throttle valve 7.

The engine is provided with a turbocharger 11. The turbocharger 11 has a coaxial connection between a compressor 12 for compressing intake air and a turbine 13 for absorbing a driving force of the compressor 12 from exhaust energy. To prevent the supercharging pressure from exceeding the set pressure, the exhaust gas at the inlet of the turbine 13 is
The waste gate valve 15 which bypasses and flows is provided.

In order to extract a part of the exhaust gas from the exhaust passage 3 and recirculate the exhaust gas to the intake passage 2, a primary EGR passage 31 communicating the upstream of the turbine 13 and the downstream of the throttle valve 7.
And a secondary EGR passage 32 that connects the downstream of the turbine 13 and the upstream of the compressor 12 with two EGR passages. The EGR passages 31 and 32 are driven by step motors 34 and 36 (EGR valve control devices). EGR valves 33 and 35 are provided.

The signals from the accelerator operation amount from the accelerator sensor 22 (depression amount of the accelerator pedal), the position signal for each unit crank angle from the crank angle sensor 23, and the reference position signal are transmitted to the air flow meter 24.
Is input to the control unit 21 together with the respective signals of the intake air flow rate from the cooling water temperature from the water temperature sensor 25,
The control unit 21 operates the lean air-fuel ratio in a predetermined operation region by simultaneously controlling the throttle valve opening and the injection amount from the fuel injection valve, and improves the output even when the lean air-fuel ratio is operated. In order to suppress the NOx that increases due to this supercharging while performing supercharging,
Two EGR valves 3 via step motors 34 and 36
The opening degree of 3, 35 is controlled.

In this case, if the opening area of the throttle valve 7 and the opening areas of the EGR valves 33 and 35 are independently calculated, fresh air (air taken in through an air cleaner) is calculated by a change in the opening area of the throttle valve 7. (The EGR gas is not included.) When the flow rate changes, the flow rate of the fresh air sucked into each cylinder and the flow rate of the EGR gas do not match. In order to reduce NOx, a target EGR rate according to the operating conditions of the engine is predetermined, but the flow rate of fresh air and E
If the phase with the flow rate of the GR gas does not match, the actual EG
The R rate deviates greatly from the target value, and N
Ox will increase and the combustion stability of the engine will be greatly impaired.

To cope with this, the control unit 21 sets two EGRs, a primary and a secondary, based on a target fresh air flow rate based on the accelerator operation amount and the engine speed, and a target EGR rate corresponding to the engine operating conditions.
The target flow rates of the valves 33 and 35 are calculated, the total gas flow rate supplied to the engine is calculated based on the target flow rate and the target fresh air flow rate, and the total opening area according to the total gas flow rate is calculated. The total opening area is distributed to the target opening area of the throttle valve and the target opening areas of the two EGR valves 33 and 35.

The contents of the control executed by the control unit 21 will be described with reference to the following flowchart.

FIG. 2 shows a throttle valve 7 and two EGR valves 3
This is for calculating each of the target opening degrees 3 and 35, and is executed at regular intervals (for example, every 10 msec). Here, FIG. 2 is configured as the main routine, and FIGS. 6 and 9 are configured as the subroutine of FIG. 2. Therefore, the subroutine will be described below when a certain step of the subroutine occurs during the description of the main routine.

In step 1 of FIG. 2, the target fresh air flow rate t of the throttle valve is determined based on the accelerator operation amount and the engine speed.
Calculate Qa. This may be obtained by searching a map having the contents shown in FIG. 3 from the accelerator operation amount and the engine speed.

In step 2, a target EGR rate tRgr is calculated. The target EGR rate is determined based on combustion stability and exhaust gas (NOx).
It is determined from the engine performance such as the reduction rate and the fuel consumption improvement cost, and the requirements are different for each operating condition of the engine. However, here, for the sake of simplicity, it is assumed that the map is obtained by searching a map having the contents shown in FIG. 4 from the engine load and the engine speed.

In step 3, the primary EGR valve 3
3. Calculate each target flow rate of the secondary EGR valve 35 (abbreviated as “P / S-EGR / V target flow rate” in the figure).
This calculation will be described with reference to the subroutine of FIG.

In step 1 of FIG. 6, the target fresh air flow rate tQa
And the target EGR rate tRegr

[0035]

## EQU1 ## The total EGR flow rate tQegr is calculated by the equation tQegr = tQa × tRegr.

In step 2, the total EGR flow rate tQe
gr and the above-described target fresh air flow rate tQa at the same time (P-EGR / V in the figure)
) Is calculated, and the difference between the pressure difference and the maximum opening area Apegr of the primary EGR valve is calculated. In step 3, based on the max (constant value), the maximum flow rate Qpegr of the primary EGR valve Calculate max.

Here, the maximum flow rate of the primary EGR valve is determined by the pressure ratio Pm / Pex before and after the primary EGR valve.
(Where Pm is the intake pressure and Pex is the exhaust pressure), it can also be obtained by a theoretical calculation formula. Here, for simplicity, a table containing the contents of FIG. 8 from the pressure ratio Pm / P0 to the atmospheric pressure is used. The flow coefficient Kv is obtained by searching for
And using this flow coefficient Kv,

[0038]

## EQU2 ## Qpegr max = Kv × Apegr The maximum flow rate Qpegr of the primary EGR valve is obtained by the expression of max.
Calculate max.

The pressure ratio Pm / P0 between the intake pressure Pm and the atmospheric pressure P0 is represented by a target fresh air flow rate tQa and a total EGR flow rate tQa.
A map containing the contents shown in FIG. 7 may be retrieved from the total gas flow rate and the engine speed, with the sum of Qegr as the total gas flow rate.

In step 4, the maximum flow rate Qpegr of the primary EGR valve is set. max and total EGR flow rate tQeg
Compare r. Qegr> Qpegr In the case of max, even if the primary EGR valve is fully opened, the total EGR flow rate is insufficient, so the secondary EGR valve needs to be opened. Therefore, in this case, the process proceeds to steps 5 and 6, and the maximum flow rate Qpegr of the primary EGR valve is set. max is set to the target flow rate tQpegr (= Qpeg) of the primary EGR valve.
r max) and the target flow rate tQsegr (= tQegr) of the secondary EGR valve with respect to the total EGR flow rate tQegr that is insufficient with the maximum flow rate of the primary EGR valve alone.
gr-Qpegr max).

On the other hand, tQegr ≦ Qpegr If it is max, the total EGR flow rate t is determined only by the primary EGR valve.
Since Qegr is covered, the process proceeds from Step 4 to Steps 7 and 8, where the total EGR flow rate tQegr is set to the target flow rate tQpegr for the primary EGR valve, and the target flow rate tQsegr for the secondary EGR valve is set to 0.

In this manner, the target flow rates tQpeg of the two primary and secondary EGR valves 33 and 35 are set.
After obtaining r and tQsegr, returning to FIG. 2, in steps 4 and 5, the target flow rates tQpegr and tQsegr are converted into a new air flow rate based on the physical properties of the exhaust gas. The total gas flow rate is calculated based on the new air flow rate, the total opening area is calculated in accordance with the calculated total gas flow rate, and the three ratios of the target fresh air flow rate to the total gas flow rate and the EGR valve target flow rate are calculated. The respective target opening areas of the three valves 7, 33, 35 are calculated according to the total opening area.

The processing of steps 4 and 5 will be described with reference to the subroutine of FIG.

In step 1 of FIG. 9, the primary EGR
A coefficient Kpegr for converting the target flow rate tQpegr of the valve into a new air flow rate based on the physical property value of the exhaust gas is calculated, and a value obtained by multiplying the target flow rate tQpegr of the primary EGR valve by the new air flow rate conversion coefficient Kpegr in step 2 is calculated. New air flow rate conversion value Q of target flow rate of primary EGR valve
It is calculated as pega.

The fresh air flow rate conversion coefficient Kpegr can be theoretically calculated as a function of the exhaust pressure and the exhaust temperature, the intake pressure and the intake temperature, etc., but these state quantities are determined by the operating conditions of the engine. Therefore, for simplicity here,
What is necessary is just to obtain | require by searching the map which contains FIG. 10 from engine load and engine speed. FIG.
0 is actual machine data.

In Steps 3 and 4, similarly to Steps 1 and 2, the secondary EGR valve (in the figure, "S-EGR
/ V "), a coefficient Ksegr for converting the target flow rate into a new air flow rate based on the physical properties of the exhaust gas is calculated, and a value obtained by multiplying this target flow rate tQsegr of the secondary EGR valve by this new air flow rate conversion coefficient Ksegr. The secondary EG
It is calculated as a fresh air flow rate conversion value Qsega of the target flow rate of the R valve.

The new air flow rate conversion coefficient Ksegr can be theoretically calculated as a function of the exhaust pressure and the exhaust temperature, the supercharging pressure and its temperature, and the like. However, since these state quantities are determined by the operating conditions of the engine, The actual machine data is measured as shown in FIG. 11 according to the load and the engine speed, a map is formed based on the actual machine data, and the map may be searched for.

Although FIG. 11 shows the same characteristics as FIG. 10, the pressure and temperature of the EGR gas flowing through the primary EGR valve 33 are higher than the EGR gas flowing through the secondary EGR valve. 11 has gentler characteristics.

In step 5 of FIG. 9, the total gas flow rate tQgas (= tQa + Qp) is calculated by summing the target fresh air flow rate tQa and the two new air flow rate conversion values thus obtained.
ega + Qsega), and in the following step 6, the total opening area tAg based on the total gas flow rate tQgas
Calculate as.

Here, the value obtained by dividing the throttle valve opening area Aa by the rotational speed Ne and the displacement Ve is the normalized opening area ADN.
This ADNV is plotted on the horizontal axis as V, and the maximum value Qgas for each rotation speed of the intake flow rate (intake amount per unit time) tQgas per cycle (in a 4-cylinder engine, a section of 720 degrees in crank angle) is taken. The ratio with respect to the maximum intake air flow rate ratio QH0st (= tQgas / Qgas) max),
Taking this reference intake flow rate ratio QH0st on the horizontal axis, FIG.
As shown in (1), the correlation between the normalized opening area and the reference intake air flow ratio is uniquely determined regardless of the engine speed or the displacement.

From this, a reference intake flow rate ratio QH0st is calculated based on the total gas flow rate tQgas, and a normalized opening area ADNV is obtained by searching a table containing the contents of FIG. 12 from the reference intake flow rate ratio QH0st. Using this normalized opening area ADNV

[0052]

## EQU3 ## The total opening area tAgas can be calculated by the equation tAgas = ADNV × Ne × Ve.

In Steps 7 and 8 in FIG. 9, three ratios of the target fresh air flow rate tQa and the respective fresh air flow rate conversion values Qpega and Qsega with respect to the total gas flow rate tQgas are calculated, and the ratios thus obtained are calculated. And the above total opening area t
Using Agas,

[0054]

## EQU4 ## tAa = tAgas.times. (TQa / tQgas) tApegr = tAgas.times. (Qpega / tQga)
s) tAsegr = tAgas × (Qsega / tQga
s), the target opening area tAa of the throttle valve 7, the target opening area tApegr of the primary EGR valve 33,
Target opening area tAsegr of secondary EGR valve 35
Are respectively calculated.

After the calculation of the target opening areas of the throttle valve 7 and the two primary and secondary EGR valves 33 and 35 is completed, the flow returns to FIG. 2 again. Target opening of valve 7 and two EGR valves 3 for primary and secondary
The respective target step numbers of 3, 35 (corresponding to the target opening) are calculated. For example, in the case of the throttle valve 7, a correlation between the opening area and the opening degree shown in FIG. 5, which is determined by the shape and dimensions of the throttle body and the throttle valve for each part, is stored in a table, and this table is searched. Can be obtained by Also, the step motor type EGR valves 33, 3
In the case of 5, the correlation between the opening area and the number of steps determined for each part is made into a table, and the target number of steps (corresponding to the target opening) may be obtained by searching this table.

The signal of the throttle valve target opening obtained in this way is output to the throttle valve controller 8, whereby the throttle valve controller 8 makes the actual opening of the throttle valve 7 coincide with the target opening. The throttle valve 7 is driven.

A signal corresponding to the target opening of the primary EGR valve 33 is output to a step motor 34 which is an EGR valve control device.
Drives the primary EGR valve 33 so that the actual opening of the primary EGR valve 33 matches the target opening. Similarly, a signal corresponding to the target opening of the secondary EGR valve is output to the stepping motor 36, whereby the stepping motor 36 controls the secondary EGR valve 35 so that the actual opening of the secondary EGR valve 35 matches the target opening.
The GR valve 35 is driven.

Next, the operation of the present embodiment will be described with reference to FIG.

In this embodiment, the target fresh air flow rate tQa is determined based on the accelerator operation amount and the engine speed, and the target EGR rate tReg is determined based on the engine load and the engine speed.
r, the total EGR flow rate tQegr is determined from these values, and the maximum EGR flow rate Qpegr of the primary EGR valve 33 By comparison with max, the total EGR flow rate t
Qegr is the target flow rate tQ of the primary EGR valve 33.
pegr and the target flow rate tQs of the secondary EGR valve 35
egr. The total gas flow rate tQgas supplied to the engine is calculated based on the target flow rates tQpegr and tQsegr of these two EGR valves and the target fresh air flow rate tQa of the throttle valve, and the total gas flow rate tQg
The total opening area tAgas is determined in correspondence with “as”, and based on the total opening area tAgas, the target opening areas tAa, tApegr, and tAsegr of the throttle valve 7, the primary EGR valve 33, and the secondary EGR valve 35 are calculated.

As described above, according to the present embodiment, the total opening area tAgas at which the target fresh air flow rate and the target EGR rate can be obtained.
Is firstly obtained and distributed to the target opening area of the throttle valve and the target opening areas of the two EGR valves, so that the fresh air flow required from the engine torque and the air-fuel ratio and the EGR required for NOx reduction are obtained. Both the rate and the rate can be realized with high accuracy, whereby both the drivability of the vehicle and the reduction of NOx can be satisfied.

The total EGR flow rate tQegr is calculated based on the target fresh air flow rate and the target EGR rate.
The maximum flow rate of the primary EGR valve is calculated based on the pressure difference between the front and rear of the R valve. When the total flow rate of the primary EGR valve exceeds the maximum flow rate of the primary EGR valve, the maximum flow rate of the primary EGR valve is reduced. It becomes the target flow rate and the primary E
The remainder after subtracting the maximum flow rate of the GR valve is the secondary EG
It becomes the target flow rate of the R valve. On the other hand, when the total EGR flow rate is equal to or less than the maximum flow rate of the primary EGR valve, the total EG
R flow rate becomes the target flow rate of the primary EGR valve 42,
And the target flow rate of the secondary EGR valve becomes zero.

As a result, when the engine load is low, the total EG
In a region where the R flow rate is small, a primary EGR valve having a large differential pressure across the EGR valve is used, so that a sufficient flow rate of E
The GR gas can be refluxed. In addition, when the supercharging pressure increases and the differential pressure across the EGR valve decreases, and the total EGR flow cannot be flowed only by the primary EGR valve, the EGR is performed using the secondary EGR valve. However, the total EGR flow can be flowed without excess or shortage.

If the physical property values (pressure, temperature) of the EGR gas (that is, exhaust gas) differ depending on the operating conditions of the engine,
Even with the same EGR valve opening area, the EGR flow rate (mass flow rate) differs. Therefore, if the total gas flow rate is obtained without performing physical property adjustment of the EGR gas and fresh air,
Although the calculation accuracy of the total gas flow rate decreases, according to the present embodiment, the primary EGR is performed based on the physical properties of the exhaust gas.
The target flow rate of each of the valve and the secondary EGR valve is converted to a new air flow rate, and the sum of the two new air flow rate conversion values and the target fresh air flow rate is calculated as a total gas flow rate, whereby the physical properties of the EGR gas and fresh air are matched. As a result, even if the operating conditions of the engine are different, the calculation accuracy of the total gas flow rate does not decrease.

In the embodiment, a device capable of controlling the opening of the throttle valve independently of the accelerator pedal is provided, and by simultaneously controlling the opening of the throttle valve and the amount of fuel supplied to the engine, the lean air-fuel ratio is increased. Although the EGR device of the present invention has been described as being combined with the engine that has enabled the above-mentioned operation, the EGR device of the present invention is not limited to such an engine.

For example, the two EGR passages 31 and 32 are selectively used according to the engine operating conditions. In this case, when the engine is under a low load, the secondary EGR valve 35 is used.
Is closed and the primary EGR valve 33 is opened for use.
As a result, a sufficient flow of EGR gas can be recirculated even when the engine load is low.

On the other hand, when the EGR valve is merely provided in the EGR passage communicating the downstream of the exhaust turbine and the upstream of the intake compressor, the differential pressure across the EGR valve is small and the flow rate is sufficient when the engine is under a low load. Cannot be recirculated, and the effect of reducing NOx in exhaust gas is not sufficient.

When the downstream pressure of the throttle valve 7 becomes higher than the exhaust pressure upstream of the turbine 13, the primary EGR valve 33 is closed and the secondary EGR valve 35 is opened. Thus, EGR can be performed by the secondary EGR passage 32 even when the supercharging pressure is increased.

On the other hand, in the case where only the EGR valve is provided in the passage communicating the upstream of the exhaust turbine and the downstream of the throttle valve, the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine due to supercharging. In this case, backflow occurs and EGR cannot be performed.

Of course, the two EGR passages 31 and 32 are selectively used according to the engine operating conditions. In this case, when the engine is under a low load, the secondary EGR valve 35 is used.
And the primary EGR valve 33 is opened, and when the downstream pressure of the throttle valve 7 becomes higher than the exhaust pressure upstream of the turbine 13, the primary EGR valve 33 is closed and the secondary EGR valve 35 is opened. I don't care.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of target opening degrees of a throttle valve and two EGR valves.

FIG. 3 is a characteristic diagram of a target fresh air flow rate.

FIG. 4 is a characteristic diagram of a target EGR rate.

FIG. 5 is a characteristic diagram of a throttle valve target opening.

FIG. 6 is a flowchart for explaining calculation of each target flow rate of two EGR valves.

FIG. 7 is a characteristic diagram of an intake pressure ratio.

FIG. 8 is a characteristic diagram of a flow coefficient.

FIG. 9 is a flowchart for explaining the calculation of each target opening area of a throttle valve and two EGR valves.

FIG. 10 is a characteristic diagram of a fresh air flow rate conversion coefficient Kpegr.

FIG. 11 is a characteristic diagram of a fresh air flow rate conversion coefficient Ksegr.

FIG. 12 is a characteristic diagram showing a relationship between a normalized opening area and a reference intake flow rate ratio.

FIG. 13 is a waveform chart for explaining the operation of the present embodiment.

FIG. 14 is a diagram corresponding to claims of the fourth invention.

[Explanation of symbols]

Reference Signs List 4 fuel injection valve 7 throttle valve 8 throttle valve control device 11 turbocharger 21 control unit 31 primary EGR passage 32 secondary EGR passage 33 primary EGR valve 34 step motor (primary EGR valve control device) 35 secondary EGR valve 36 step motor (secondary EGR) Valve control device)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Isamu Kazama 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 3G005 EA14 FA35 GB15 GB27 GD13 GD17 GE09 HA12 HA19 JA06 JA12 JA24 JA28 JA39 JA45 JB18 3G062 BA02 ED03 ED10 ED11 GA01 GA04 GA05 GA06 GA14 GA21 GA23 3G084 BA03 BA05 BA08 BA09 BA19 BA20 CA03 DA10 FA07 FA10 FA12 FA18 FA20 FA26 FA32 FA33 FA37 3G092 AA17 AA18 BA01 BA03 BA04 DB03 DC01 DC08 DC12 DF01 HA05 HA16X HD07X HD09X HE01X HE06X HE08X

Claims (7)

[Claims] 1. A turbocharger coaxially connecting an exhaust turbine and an intake compressor, a primary EGR passage communicating an upstream of the exhaust turbine and a throttle valve downstream, a secondary EGR passage communicating a downstream of the exhaust turbine and an upstream of the intake compressor. An EGR device characterized in that these two EGR passages are selectively used according to the operating conditions of the engine, and means for shutting off the secondary EGR passage and using the primary EGR passage when the engine is under a low load are provided. 2. A turbocharger which coaxially connects an exhaust turbine and an intake compressor, a primary EGR passage communicating between an upstream of the exhaust turbine and a throttle valve downstream, and a secondary EGR passage communicating between a downstream of the exhaust turbine and an intake compressor upstream. Means for selectively using these two EGR passages according to the operating conditions of the engine, and for shutting off the primary EGR passage and using the secondary EGR passage when the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine. An EGR device characterized by the above-mentioned. A turbocharger coaxially connecting the exhaust turbine and the intake compressor; a primary EGR passage communicating the upstream of the exhaust turbine with the throttle valve downstream; a secondary EGR passage communicating the downstream of the exhaust turbine with the intake compressor upstream. These two EGR passages are selectively used according to the operating conditions of the engine. When the engine is under a low load, the secondary EGR passage is shut off and the primary EGR passage is used, and when the downstream pressure of the throttle valve becomes higher than the exhaust pressure upstream of the exhaust turbine. Means for interrupting the primary EGR passage and using the secondary EGR passage. 4. An engine provided with a turbocharger in which an exhaust turbine and an intake compressor are coaxially connected, wherein a device capable of controlling the opening of a throttle valve independently of an accelerator pedal communicates with an upstream of the exhaust turbine and a downstream of the throttle valve. EG
A primary EGR valve for opening and closing the R passage, a device capable of controlling the degree of opening of the primary EGR valve, a secondary EGR valve for opening and closing an EGR passage communicating the downstream of the exhaust turbine and the upstream of the intake compressor, and a secondary EGR valve. A device capable of controlling the opening, a means for calculating a target fresh air flow rate based on an accelerator operation amount, a means for calculating a target EGR rate corresponding to an engine operating condition, a target fresh air flow rate and a target EGR rate From the two EG
Means for calculating each target flow rate of the R valve; means for calculating the total gas flow rate supplied to the engine based on the target flow rates of these two EGR valves and the target fresh air flow rate; Means for calculating the total opening area; means for calculating the target opening areas of the throttle valve and the two EGR valves based on the total opening area; and the throttle valve so that the target opening area of the throttle valve becomes the target opening area. Means for driving a control device; means for driving the primary EGR valve control device to have the target opening area of the primary EGR valve; and the secondary EGR valve control device to have the target opening area of the secondary EGR valve. And a means for driving the engine. 5. A means for calculating each target flow rate of two EGR valves, means for calculating a total EGR flow rate based on the target fresh air flow rate and the target EGR rate, and a primary EG.
Means for calculating the differential pressure across the R valve; means for calculating the maximum flow rate of the primary EGR valve based on the differential pressure; and, when the total EGR flow rate exceeds the maximum flow rate of the primary EGR valve, the primary EGR valve Is the maximum flow rate of the primary EGR valve and the total EG
The remainder obtained by subtracting the maximum flow rate of the primary EGR valve from the R flow rate is set as the target flow rate of the secondary EGR valve. When the total EGR flow rate is equal to or less than the maximum flow rate of the primary EGR valve, the total EGR flow rate is set to the primary EGR valve. 42 and the secondary EG
5. The engine control device according to claim 4, further comprising means for setting a target flow rate of the R valve to zero. 6. The means for calculating the total gas flow rate includes a primary EGR valve and a secondary EGR valve based on physical properties of exhaust gas.
Means for converting each target flow rate of the GR valve into a new air flow rate, and means for calculating the sum of the two new air flow rate conversion values and the target fresh air flow rate as the total gas flow rate. Item 6. An engine control device according to item 4 or 5. 7. The total opening area is defined by three ratios of a target fresh air flow rate to the total gas flow rate, a new air flow rate converted value of a target flow rate of a primary EGR valve, and a new air flow rate converted value of a target flow rate of a secondary EGR valve. 7. The engine control device according to claim 6, wherein the target opening area of the throttle valve, the target opening area of the primary EGR valve, and the target opening area of the secondary EGR valve are calculated by multiplying the target opening area by multiplication.