JP4013766B2 - Engine exhaust gas recirculation control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control device for an engine (internal combustion engine).
[0002]
[Prior art]
Internal EGR gas amount control means for controlling the amount of internal EGR gas in the combustion chamber; external EGR gas amount control means for controlling the amount of external EGR gas that recirculates part of the exhaust gas from the exhaust system to the intake system through the external recirculation passage; A water-cooled cooler for cooling the external EGR gas,
(1) When the engine is under low load, the amount of internal EGR gas at a relatively high temperature is increased, the suction negative pressure in the cylinder during the intake stroke is reduced to reduce the pumping loss, and the operation of the water-cooled cooler is stopped. To ensure the stability of combustion by keeping the intake mixture temperature high,
(2) When the load is high, the combustion temperature is lowered by increasing the amount of external EGR gas cooled by the water-cooled cooler, reducing NOx, reducing the thermal load, and suppressing the occurrence of knocking.
As a result, there is a technique for preventing the occurrence of knocking while simultaneously reducing the pumping loss at the time of low load and the heat load at the time of high load (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-4-175449
[0004]
[Problems to be solved by the invention]
By the way, an increasing number of intake parts made of an intake collector and an intake manifold are made of resin. This is because the heat conductivity of the resin is lower than that of aluminum, so that the temperature of the intake air is less likely to increase than that of aluminum, and the charging efficiency is improved correspondingly and the weight is light.
[0005]
On the other hand, fuel efficiency has been improved by introducing external EGR gas or leaving the internal EGR gas in the combustion chamber to reduce the pumping loss. However, in order to further improve fuel efficiency, There is a growing demand for the introduction of many external EGR gases.
[0006]
However, when the amount of external EGR gas is increased for an engine equipped with the above-described resin intake parts, the resin intake parts are exposed to high temperature external EGR gas, particularly when the engine is under high load, and durability is reduced. (Heat damaged).
[0007]
Since the component heat-resistant upper limit temperature required for resin-made air intake components is known in advance so as not to be damaged by heat, the EGR cooler cools the high-temperature external EGR gas at the time of high engine load to below the component heat-resistant upper limit temperature. However, the heat-resistant upper limit temperature of parts is about 170 ° C for resin, for example, and if the external EGR gas is cooled to such a low temperature when the engine is heavily loaded, the combustion stability at the time of high engine load deteriorates. To do. If the amount of fuel is increased in order to recover from the deterioration of the combustion stability, the fuel efficiency improvement effect by EGR is reduced.
[0008]
Therefore, the present invention is directed to an engine in which air is introduced into a combustion chamber via a resin intake part, and uses an external EGR device and an internal EGR device. By changing the share ratio between the external EGR rate) and the internal EGR gas amount (or internal EGR rate) and increasing the share rate of the internal EGR gas amount as the load increases, even under a large load EGR condition at high load It aims at maintaining the fuel consumption improvement effect, suppressing the heat damage to the resin air intake parts.
[0009]
On the other hand, the above-mentioned conventional device is not intended for an engine having a resin intake part, and at the time of high load, unlike the present invention, increases the amount of external EGR gas and decreases the amount of internal EGR gas. I am letting. As described above, the above-described conventional apparatus is different in technical idea from the present invention in that the target engine is different and the control direction of the external and internal EGR gas amounts is reversed.
[0010]
[Means for Solving the Problems]
The present invention It consists of an intake collector and an intake manifold In an engine in which air is introduced into a combustion chamber via an intake part formed of resin, An EGR passage that communicates the exhaust passage and the intake manifold, an EGR valve that can adjust the amount of exhaust that flows to the intake manifold via the EGR passage, and an actuator that drives the EGR valve An external EGR device capable of adjusting an external EGR rate or an external EGR gas amount; an internal EGR device capable of adjusting an internal EGR rate or an internal EGR gas amount; Out of the EGR area where the external EGR gas is introduced, there is a possibility of causing heat damage to the resin intake parts and an area causing heat damage to the resin intake parts. The share ratio between the external EGR rate or external EGR gas amount and the internal EGR rate or internal EGR gas amount is changed according to the engine load state, and the share ratio of the external EGR rate or external EGR gas amount is increased as the load becomes higher. A sharing ratio control means for decreasing and increasing the sharing ratio of the internal EGR rate or the internal EGR gas amount.
[0011]
In addition, an external EGR gas cooling device that cools the external EGR gas by causing heat exchange between the external EGR gas and the refrigerant is provided, and the external EGR rate or the share ratio of the external EGR gas amount is increased as the load becomes higher. When decreasing, the flow rate of the refrigerant flowing through the external EGR gas cooling device is reduced to a flow rate at which the combustion stability does not deteriorate.
[0012]
【The invention's effect】
By introducing a larger amount of external EGR gas than in the past at the time of high load, a further improvement in fuel efficiency can be obtained due to a reduction in pumping loss. On the other hand, it is formed from a material other than metal, such as a resin, by high temperature external EGR gas at the time of high load. However, in the present invention, the higher the load, the lower the share ratio of the external EGR rate (or external EGR gas amount) and the share ratio of the internal EGR rate (or internal EGR gas amount). Therefore, the heat damage to the resin intake parts can be suppressed, and the fuel efficiency is reduced by the decrease in the external EGR rate, and the fuel efficiency improvement effect can be maintained because the increase in the internal EGR rate is compensated.
[0013]
As described above, according to the present invention, a remarkable fuel efficiency improvement effect can be maintained while suppressing heat damage to the resin intake parts even under a large amount of EGR conditions at high load.
[0014]
Further, when the sharing ratio of the external EGR rate (or external EGR gas amount) is decreased as the load becomes higher, the refrigerant flow rate flowing to the external EGR gas cooling device is the same as before the sharing ratio of the external EGR rate is decreased. The cooling of the external EGR gas becomes relatively strong and the combustion stability at the time of high load is deteriorated. However, according to the present invention, the combustion is reduced when the share of the external EGR rate is reduced as the load becomes higher. Since the flow rate of the refrigerant flowing through the external EGR gas cooling device is reduced to a flow rate at which the stability does not deteriorate, the combustion stability is not impaired.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a schematic diagram for explaining the system of the present invention.
[0017]
The air is introduced into the combustion chamber 5 of each cylinder through a resin-made intake part composed of the intake collector 2 and the intake manifold 3. Fuel is injected and supplied from a fuel injector 21 disposed in the intake port 4 of each cylinder. The fuel injected into the air is vaporized and mixed with air to form a gas (air mixture) and flows into the combustion chamber 5. This air-fuel mixture is confined in the combustion chamber 5 when the intake valve 15 is closed, and is compressed by the rise of the piston 6.
[0018]
In order to ignite this compressed air-fuel mixture with a high-pressure spark, an ignition device 11 of an electronic power distribution system is provided in which an ignition coil with a built-in power transistor is arranged in each cylinder. The ignition device 11 includes an ignition coil 13 that stores electric energy from the battery, a power transistor that supplies and cuts off the primary side of the ignition coil 13, and an ignition plug 14 that is provided on the ceiling of the combustion chamber 5. .
[0019]
The ignition timing that provides the best fuel efficiency is determined as the basic ignition timing. The engine controller 31 calculates the basic ignition timing according to the operating conditions (engine load and rotational speed), and the actual crank angle is set to this ignition timing. When they coincide, the ignition timing is controlled by cutting off the primary current of the spark plug 14 via the power transistor 13. This ignition timing is slightly before the compression top dead center. When a spark is blown by the spark plug 14 and the compressed air-fuel mixture in the combustion chamber 5 is ignited, the flame spreads and eventually explosively burns, and the gas generated by this combustion. The pressure works to push down the piston 6. This work is taken out as the rotational force of the crankshaft 7. The combusted gas (exhaust gas) is discharged into the exhaust passage 8 when the exhaust valve 16 is opened.
[0020]
A three-way catalyst 9 is provided in the exhaust passage 8. When the air-fuel ratio of the exhaust gas is in a narrow range (window) centered on the stoichiometric air-fuel ratio, the three-way catalyst 9 can efficiently remove harmful three components such as HC, CO, and NOx contained in the exhaust gas simultaneously. Since the air-fuel ratio is the ratio of the intake air amount and the fuel amount, the intake air amount introduced into the combustion chamber 5 per one cycle of the engine (crank angle 720 ° section in a four-cycle engine) and the fuel injector 21 The engine controller 31 uses the intake air flow rate signal from the air flow meter 32 and the fuel from the fuel injector 21 based on the signals from the crank angle sensors (33, 34) so that the ratio to the fuel injection amount becomes the stoichiometric air-fuel ratio. The injection amount is determined and the O provided upstream of the three-way catalyst 9 ₂ The air-fuel ratio is feedback controlled based on a signal from a sensor (not shown).
[0021]
An intake throttle valve 23 is driven by a throttle motor 24 upstream of the intake collector 2 and is equipped with a so-called electronically controlled throttle 22. Since the torque required by the driver appears in the amount of depression of the accelerator pedal 41 (accelerator opening), the engine controller 31 determines a target torque based on a signal from the accelerator sensor 42, and a target air for realizing this target torque. The amount is determined, and the opening degree of the intake throttle valve 23 is controlled via the throttle motor 24 so that this target air amount is obtained.
[0022]
EGR device (external EGR device) is provided mainly to improve fuel efficiency. The EGR device determines the amount (or rate) of the EGR passage 25 that communicates the exhaust passage 8 and the intake manifold 3, and the exhaust gas that flows to the intake manifold 3 through the EGR passage 25, that is, the inert gas (external EGR gas). When the EGR valve 26 that can be adjusted and an actuator 27 (for example, a step motor) that drives the EGR valve 26 are introduced and the external EGR gas is introduced into the intake manifold 3, the pumping loss is reduced and the fuel efficiency is improved.
[0023]
An intake valve timing control mechanism (hereinafter referred to as “VTC mechanism”) that can continuously control the phase of the intake valve cam with a constant operating angle in order to leave the inert gas (internal EGR gas) in the combustion chamber 5. 29) (internal EGR device). That is, a cam sprocket and a crank sprocket are attached to the front portions of the intake valve camshaft 28 and the crankshaft 7, respectively, and a timing chain (not shown) is hung around these sprockets so that the intake valve camshaft 28 is Although driven by the crankshaft 7 of the engine, a VTC mechanism 29 is provided between the cam sprocket and the intake valve camshaft 28. In this VTC mechanism 29, when no signal is given to the VTC mechanism actuator, the intake valve camshaft 28 is at the most retarded position, and the more the amount of control given to the VTC mechanism actuator is increased, the greater the amount of control given to the cam sprocket. 28 rotates to the advance side. The rotation angle of the intake valve camshaft 28 is hereinafter referred to as “cam phase”.
[0024]
When the cam phase, that is, the opening / closing timing of the intake valve 15 is changed, the amount of internal EGR gas remaining in the combustion chamber 5 changes. As the amount of internal EGR gas in the combustion chamber 5 increases, the pumping loss decreases and fuel efficiency improves.
[0025]
The EGR valve 27 and the VTC mechanism 29 are equivalent in the sense that an inert gas is introduced into the combustion chamber 5. In order to distinguish the EGR rate realized by both, the EGR rate realized by the EGR valve 27 is called “external EGR rate”, and the EGR rate realized by the VTC mechanism 29 is called “internal EGR rate”.
[0026]
The EGR passage 25 includes an EGR cooler 55 (external EGR gas cooling device). This is for cooling the external EGR gas. The EGR cooler 55 has a double structure consisting of an inner tube and an outer tube, and external EGR gas flows through the inner tube and engine coolant (refrigerant) flows through the outer tube. Although only a part of the cooling water flow path is shown in FIG. 1, the entire cooling water flow path is as shown in FIG. 2, and the flow path 54 bypasses the main flow path 53 to the engine 1 (water jacket). An EGR cooler 55 is interposed between the two. Reference numeral 51 denotes a radiator that cools the cooling water heated by the engine, and reference numeral 52 denotes a water pump that pumps the cooling water cooled by the radiator 51 toward the engine.
[0027]
Further, the bypass passage 54 is provided with a flow rate control valve 56 for adjusting the flow rate of the cooling water flowing through the EGR cooler 55.
[0028]
Now, in order to significantly improve fuel consumption, it has been requested to introduce more external EGR gas.
[0029]
However, when increasing the amount of external EGR gas for an engine equipped with a resin intake part, it is necessary to consider thermal damage to the resin intake part.
[0030]
Therefore, when examining the relationship between the EGR region into which the external EGR gas is introduced and the heat damage to the resin intake parts, as shown in FIG. 3, the operation region can be roughly divided into four parts. It was found that the heat damage to the plastic air intake parts is as follows. In the present invention, the EGR region into which the external EGR gas is introduced is larger than that of the conventional device, and the external EGR rate in each region is larger than that of the conventional device.
[0031]
Region R1: A region where heat damage to the resin intake parts is not a problem.
[0032]
Region R2: A region that may cause heat damage to the resin-made air intake parts (a region in which melting damage does not occur in a short time but melts due to accumulation of thermal fatigue).
[0033]
Region R3: a region that causes thermal damage to the resin intake parts (region where melting damage occurs in a short time).
[0034]
Region R4: The region where heat damage to the resin intake parts does not matter because no external EGR gas is introduced.
[0035]
That is, the region R1 has the largest external EGR rate in the low / medium load region and the low / medium rotational speed region. On the other hand, the remaining regions R2, R3, and R4 are all in a high load region and a high rotation speed region, and this region is divided into three regions R2, R3, and R4 from the low load side and the low rotation side. In the region R4, the external EGR gas is not introduced, that is, the external EGR rate = 0, so that the external EGR rate is increased in this order for the remaining two regions R3 and R2.
[0036]
On the other hand, the exhaust temperature is the lowest in the region R1, and is higher in the regions R2 and R3 on the high load side (for example, approximately less than 130 ° C. in the region R1, 130 ° C. or more and less than 170 ° C. in the region R2, and 170 ° C. or more in the region R3). ). Since the external EGR gas becomes high in the regions R2 and R3, the external EGR gas is cooled to some extent by the EGR cooler 55. However, in the region R3, the resin intake parts are melted in a short time, and in the region R2, the external EGR gas is short. Although there is no erosion over time, erosion occurs due to the accumulation of thermal fatigue.
[0037]
Therefore, the engine controller 31 sets an external EGR rate basic value Pegr0 in accordance with the engine load and the rotational speed so that a large amount of external EGR rate can be achieved over a wide range with the aim of further improving fuel efficiency. The EGR valve opening is calculated based on the value Pegr0, the EGR valve actuator 27 is controlled so as to be the EGR valve opening, and whether or not the operating condition is in the region R2 or R3 is determined. When in the region R2 or R3, the heat receiving amount Smheat from the external EGR gas of the resin intake part is calculated (estimated) based on the engine load, the rotational speed, and the intake air flow rate for each of the regions R2 and R3. When Smheat exceeds the predetermined heat resistance requirement criteria X, the share ratio of the external EGR rate is reduced. Allowed and increases the distribution ratio of the internal EGR rate. That is, the external EGR rate is reduced and the decrease in the external EGR rate is compensated by the increase in the internal EGR rate so that the fuel efficiency improvement effect does not change in total.
[0038]
The variable control of the external EGR rate and the share ratio of the internal EGR rate will be further described with reference to FIGS. 4 and 5. FIG. 4 shows the change in the steady operation state in the region R2, and FIG. 5 shows the change in the steady operation state in the region R3. It is a waveform diagram shown as a model.
[0039]
In FIG. 4, in region R2, external EGR gas having a high flow rate (for example, 130 ° C. to 170 ° C.) according to the external EGR rate basic value Pegr0 is introduced into the resin intake component. The amount of heat Smheat received by the intake component increases, and eventually reaches the component heat resistance requirement criterion X at t1 (see the first stage in FIG. 4). At this time, in order to lower the external EGR rate from the basic value Pegr0 to the external EGR rate P'egr2 after the target reduction (see the second stage in FIG. 4), the external value after the target reduction from the value of the EGR valve opening relative to the basic value Pegr0. The EGR valve opening is reduced to the value of the EGR valve opening with respect to the EGR rate P′egr2 (see the third stage in FIG. 4). As a result, the actual external EGR rate decreases with a predetermined slope, and catches up with the external EGR rate P′egr2 after target reduction at t2. The period from t1 to t2 is a transition period. This is because the EGR valve actuator 27 has a response delay, and the EGR valve 26 cannot be closed at a speed higher than the maximum speed of the EGR valve actuator 27.
[0040]
Further, the cooling water flow rate of the EGR cooler 55 is reduced in response to the external EGR rate being reduced from t1 (see the fourth stage in FIG. 4). This is to avoid this because the amount of cooling by the EGR cooler 55 becomes too large unless the cooling water flow rate is decreased, and the combustion stability in the region R2 which is a high load region is deteriorated. Therefore, the flow rate reduction allowance Qegrc2 of the cooling water flow rate is limited to a flow rate that does not deteriorate the combustion stability in the region R2.
[0041]
On the other hand, the internal EGR rate is changed from t1 to the target internal EGR rate Piegr so that the same good fuel economy improvement effect is maintained before and after t1. 2 The target internal EGR rate Piegr at t2 2 (See the fifth stage in FIG. 4), the cam phase is advanced with a predetermined inclination from the most retarded position to the value of the cam phase with respect to the target internal EGR rate Piegr2, and at t2, the target internal EGR rate Piegr 2 (See the sixth stage in FIG. 4).
[0042]
By reducing the external EGR rate in this way and increasing the internal EGR rate instead, the external EGR gas temperature that was 130 to 170 ° C. is lower than t1 as shown in the bottom of FIG. Thus, it is possible to avoid the occurrence of thermal fatigue in the resin intake parts.
[0043]
Next, turning to FIG. 5, the whole is the same as FIG. Therefore, here, the difference from FIG. 4 is mainly described. In the region R3, the external EGR gas temperature is higher than that in the region R2 (for example, 170 ° C. or more), so the slope of the heat reception amount Smheat is steeper than in the region R2. Yes (see the top row in FIG. 5), the time required to reach the part heat resistance requirement criteria X is short. Further, the target internal EGR rate Piegr3 in the region R3 is larger than the target internal EGR rate Piegr2 in the region R2 (see the fifth row in FIG. 5).
[0044]
In the region R3, similarly to the region R2, by reducing the external EGR rate and increasing the internal EGR rate instead, the external EGR gas temperature that has exceeded 170 ° C. as shown in the bottom of FIG. Thus, at t4, the temperature becomes approximately 130 ° C., thereby preventing the resin intake parts from being melted.
[0045]
If the resin intake parts are thermally damaged by introducing high-temperature external EGR gas into the resin intake parts in the regions R2 and R3, the introduction of the internal EGR gas is not dependent on the introduction of the external EGR gas from the beginning. Can only be considered. However, at this time, in order to maximize the internal EGR rate in the region R1, it is necessary to increase the amount of overlap of intake and exhaust. However, if the amount of overlap is increased in the region R1 that is originally in a low temperature state, it is stable. Can't get burnt. Therefore, it can be said that it is preferable to first introduce the external EGR gas and reduce the external EGR rate and increase the internal EGR rate in the regions R2 and R3 where there is a possibility of causing thermal fatigue or melting damage.
[0046]
The variable control of the share ratio of the external EGR rate and the internal EGR rate executed by the engine controller 31 will be described in detail with reference to the flowchart shown below.
[0047]
FIG. 6 is for setting a flag (hereinafter simply referred to as a “decrease flag”) for instructing a decrease in the external EGR gas flow rate, and is executed at regular intervals (for example, every 10 msec).
[0048]
In step 1, the engine rotational speed Ne detected by the crank angle sensors 33 and 34, the basic injection pulse width Tp, and the intake air flow rate QA detected by the air flow meter 32 are read. Here, Tp is a value calculated in the calculation flow of the fuel injection amount and is an engine load equivalent amount.
[0049]
In step 2, it is checked whether or not the operating conditions (Ne, Tp) are in the region R2 or R3 shown in FIG. If the operating condition becomes the region R2 or R3, the current process is terminated.
[0050]
When the operating condition is in the region R2 or R3, the routine proceeds to step 3 where the reduction flag is checked. Since this reduction flag is initially set to zero when the engine is started, the routine proceeds to step 4 where the amount of heat received from the external EGR gas of the resin intake part is calculated. The calculation of the amount of heat received from the external EGR gas of the resin intake part will be described with reference to the flow of FIG.
[0051]
In FIG. 7, in step 11, the external EGR rate basic value Pegr0 is determined. For example, the external EGR rate basic value Pegr0 is calculated by searching a map having the characteristics shown in FIG. 8 from the engine speed Ne and the basic injection pulse width Tp. As described above, the area where the external EGR gas is introduced is larger than before, and the basic value of the external EGR rate is larger than before.
[0052]
In step 12, from this external EGR rate basic value Pegr0 and the intake air flow rate QA,
Qegr = QA × Pegr0 (1)
The external EGR gas flow rate Qegr is calculated by the following equation.
[0053]
In step 13, the exhaust temperature Texh is determined. For example, the exhaust temperature Texh is calculated by searching a map having the characteristics shown in FIG. 9 from the engine speed Ne and the basic injection pulse width Tp.
[0054]
In step 14, a cooling water flow rate basic value Qcool0 to be passed to the EGR cooler 55 is determined. For example, the basic value Qcool0 of the coolant flow to be passed through the EGR cooler 55 is calculated by searching a map having the characteristics shown in FIG. 10 from the engine speed Ne and the basic injection pulse width Tp.
[0055]
In step 15, the temperature decrease margin Tegrc of the external EGR gas by the EGR cooler 55 is determined based on the cooling water flow rate basic value Qcool0 and the external EGR rate basic value Pegr0. For example, the temperature decrease margin Tegrc of the external EGR gas by the EGR cooler 55 is calculated by searching a map having the characteristics of FIG. 11 from Qcool0 and Pegr0. As shown in FIG. 11, if the cooling water flow rate is the same, the larger the external EGR rate, the smaller the temperature reduction allowance. If the external EGR rate is the same, the larger the cooling water flow rate, the larger the cooling water flow rate.
[0056]
In step 16, using the exhaust temperature Texh and the temperature decrease Tegrc,
Tegr = Texh-Tegrc (2)
The temperature Tegr of the external EGR gas introduced into the resin intake part is calculated by the following equation.
[0057]
In step 17, a value obtained by multiplying the EGR gas temperature Tegr by the EGR gas flow rate Qegr is calculated as a heat receiving amount Segr per predetermined time of the resin-made intake part.
[0058]
In step 18, by integrating the amount of heat received Segr per predetermined time, that is,
Smheat = Segr + Smheat (−1) (3)
However, Smheat (−1): the previous value of Smheat,
The amount of heat received by the resin intake part after reaching the region R2 or region R3 is calculated by the following equation. The initial value of Smheat (−1) on the right side of the expression (3) is set to zero when the engine is started or immediately after entering the region R2 or R3.
[0059]
In step 19, in preparation for the next calculation, the value of Smheat which is the current value is moved to Smheat (−1) which is the previous value.
[0060]
When the heat receiving amount Smheat of the resin intake part is obtained in this way, the process returns to FIG. 6, and in step 5, the heat receiving amount Smheat of the resin intake part is compared with the threshold value X. The threshold value X is a component heat resistance requirement criterion shown in the uppermost stage of FIGS. If the received heat amount Smheat is less than the threshold value X, the current process is terminated. When the received heat amount Smheat becomes equal to or greater than the threshold value X, the process proceeds to step 6 to set the reduction flag = 1.
[0061]
12 and 13 are used to determine the external EGR rate, and are executed at regular time intervals (for example, every 10 msec).
[0062]
In step 21, the external EGR rate basic value Pegr0 is determined in the same manner as in step 11 of FIG. In step 22, the reduction flag is checked. When the reduction flag = 0, the routine proceeds to step 23, where the external EGR rate basic value Pegr0 is directly input to the external EGR rate Pegr.
[0063]
When the weight reduction flag = 1, the routine proceeds to step 24 where it is determined whether the operating condition is in the region R2 or R3. When the operating condition is in the region R2, the process proceeds to steps 25 to 34, and when it is in the region R3, the process proceeds to steps 35 to 44 in FIG. Since the processing in each region is the same, the processing in region R2 will be mainly described.
[0064]
In step 25, the transition completed flag 2 (initially set to zero) is checked. Here, if the transition is made assuming that the transitioned flag 2 = 0, at this time, the process proceeds to step 26 and it is checked whether or not the reduction flag = 1. When it is the first time since the reduction flag = 1, the routine proceeds to steps 27 and 28, and initial setting for the transition processing is performed. That is, in step 27, the external EGR rate P′egr2 after the target weight reduction determined from the requirements of the temperature at which there is no problem with thermal damage to the resin intake parts and the temperature at which combustion stability can be ensured is determined. For example, the external EGR rate P′egr2 after target reduction is calculated by searching a table having the characteristics of FIG. 14 from the external EGR rate basic value Pegr0. In FIG. 14, an alternate long and short dash line is a straight line of P′egr2 = Pegr0. Here, since it is desired to make it smaller than Pegr0 after the external EGR rate is reduced, the slope of the straight line representing the characteristic of P′egr2 is smaller than the slope of the alternate long and short dash line (see the solid line in FIG. 14).
[0065]
In step 28, the external EGR rate basic value Pegr0 is stored in the memory "PegrTR (-1)". Here, the external EGR rate is shifted from the basic value Pegr0, which is the value before the weight reduction, to P′egr2, which is the value after the weight reduction, with PegrTR representing the external EGR rate during the transition, and “PegrTR” “(−1)” represents the previous value.
[0066]
In step 29, the external EGR rate PegrTR during the transition is calculated by the following equation, and in step 30 this is compared with the external EGR rate P′egr2 after the target weight reduction.
[0067]
PegrTR = PegrTR (-1) -Degr2 (4)
However, PegrTR (−1): the previous value of PegrTR,
Degr2: a predetermined value (constant value) that determines the transition speed,
Here, the equation (4) is an equation for gradually decreasing PegrTR by a predetermined value Degr2 per calculation cycle. The predetermined value Degr2 is determined according to the driving speed of the EGR valve actuator.
[0068]
When PegrTR representing the external EGR rate during the transition does not reach the external EGR rate P′egr2 after the target reduction, the routine proceeds to step 31 where PegrTR is put into the external EGR rate Pegr. If Step 29 is repeated when the PegrTR representing the external EGR rate during the transition does not reach the external EGR rate P′egr2 after the target reduction, the PegrTR decreases by a predetermined value Degr2 and eventually the external EGR rate P ′ after the target reduction. Egr2 is reached. At this time, the process proceeds from step 30 to step 32 to set the transition completed flag 2 = 1, and at step 33, the external EGR rate P′egr2 after the target reduction is entered into the external EGR rate Pegr.
[0069]
Since the transition completed flag 2 = 1 is set, the process proceeds from step 25 to step 34 from the next time, and the external EGR rate P′egr2 after the target reduction is entered into the external EGR rate Pegr. Step 34 is a process after the migration.
[0070]
Steps 35 to 44 in FIG. 13 that are processing in the region R3 are the same as steps 25 to 34 in FIG. 12 that are processing in the region R2. That is, if “2” in steps 35 to 44 is replaced with “3”, the operations in steps 35 to 44, which are processes in the region R3, are obtained. In step 37, it is possible to secure a temperature and combustion stability that are free from thermal damage to the resin intake parts by searching a table containing the characteristics of the broken line in FIG. 14 from the external EGR rate basic value Pegr0. The external EGR rate P′egr3 after the target reduction in the region R3 determined from a request for a proper temperature is calculated. The target EGR rate P′egr3 after the target reduction in the region R3 has a smaller slope than the external EGR rate P′egr2 after the target reduction in the region R2.
[0071]
The external EGR gas flow rate (Pegr × QA) is calculated based on the external EGR rate Pegr determined in this way, and the EGR valve opening is calculated from the external EGR gas flow, and this EGR valve opening is achieved. Thus, the EGR valve actuator 27 is controlled.
[0072]
FIG. 15 is for determining the target internal EGR rate and the target cam phase, and is executed at regular time intervals (for example, every 10 msec).
[0073]
In step 51, the reduction flag is checked. When the reduction flag = 0, the routine proceeds to step 52, where the target internal EGR rate Piegr = 0 is set, and at step 53, the target cam phase θegr = 0. At this time, the VTC mechanism 29 is in the most retarded position.
[0074]
When the reduction flag = 1, the routine proceeds from step 51 to step 54 to check whether the operating condition is in the region R2 or R3. When the operating condition is in the region R2, the process proceeds to steps 55 to 57, 62, and when the operating condition is in the region R3, the process proceeds to steps 59 to 61, 62.
[0075]
Since the processing in each region is the same, the processing in region R2 will be mainly described here.
[0076]
In step 55, the external EGR rate Pegr (determined by FIGS. 12 and 13) is read, and in step 56, the target internal EGR rate in region R2 is determined as Piegr2, based on the external EGR rate Pegr. For example, the target internal EGR rate Piegr2 in the region R2 is calculated by searching a table containing the characteristics of FIG. 16 from the external EGR rate Pegr.
[0077]
As shown in FIG. 16, the target internal EGR rate Piegr2 is a value that increases as the external EGR rate Pegr decreases. The external EGR rate Pegr when the reduction flag = 1 is equal to PegrTR during the transition as described above with reference to FIGS. 12 and 13 (see steps 30 and 31 in FIG. 12), and becomes P′egr2 after the transition (FIG. 12). Steps 30, 33, steps 25, 34). PegrTR representing the external EGR rate during the transition is reduced from Pegr0 to P'egr2 (see steps 26 to 29 in FIG. 12). Accordingly, when PegrTR representing the external EGR rate during the transition becomes smaller from Pegr0 to P'egr2, the target internal EGR rate Piegr2 becomes larger than 0 according to this, according to FIG.
[0078]
In step 57, the target internal EGR rate Piegr2 in the region R2 is entered into the target internal EGR rate Piegr2.
[0079]
Steps 59 to 61 that are processing in the region R3 are the same as steps 55 to 57 that are processing in the region R2. That is, if “2” in steps 55 to 57 is replaced with “3”, the operations in steps 59 to 61 are obtained. In step 60, a target internal EGR rate Piegr3 in the region R3 is calculated by searching a table having the characteristics of the broken line in FIG. 16 from the external EGR rate Pegr. The target internal EGR rate Piegr3 in the region R3 is larger than the target internal EGR rate Piegr2 in the region R2 with respect to the same external EGR rate Pegr (see FIG. 16).
[0080]
In step 62, the target cam phase θegr of the VTC mechanism 29 is determined based on the target internal EGR rate Piegr thus determined. For example, the target cam phase θegr of the VTC mechanism 29 is calculated by searching a table having the characteristics shown in FIG. 17 from the target internal EGR rate Piegr.
[0081]
The VTC mechanism actuator is controlled so as to obtain the target cam phase θegr determined in this way.
[0082]
FIG. 18 is for determining the coolant flow rate of the EGR cooler 55, and is executed at regular time intervals (for example, every 10 msec).
[0083]
In step 71, the engine speed Ne and the basic injection pulse width Tp are read. In step 72, the coolant flow rate basic value Qcool0 of the EGR cooler 55 is determined based on these. For example, the basic value Qcool0 of the coolant flow rate of the EGR cooler 55 is calculated by searching a table having the characteristics shown in FIG. 10 from the engine speed and the basic injection pulse width Tp.
[0084]
In step 73, the reduction flag is checked. When the reduction flag = 0, the routine proceeds to step 74, where the basic value Qcool0 is entered as it is into the cooling water flow rate Qcool of the EGR cooler 55.
[0085]
When the reduction flag = 1, the routine proceeds from step 73 to step 75, where it is determined whether the operating condition is in the region R2 or R3. When the operating condition is in the region R2, the process proceeds to steps 76 to 78, and when the operating condition is in the region R3, the process proceeds to steps 79 to 81.
[0086]
Since the processing in each region is the same, the processing in region R2 will be mainly described.
[0087]
In step 76, the external EGR rate Pegr (determined by FIGS. 12 and 13) is read, and in step 77, based on the external EGR rate Pegr, the flow rate reduction allowance Qegrc2 from the cooling water flow rate basic value Qcool0 in the region R2 is calculated. In step 78, the cooling water flow rate Qcool to be passed through the EGR cooler 55 is calculated by the following equation.
[0088]
Qcool = Qcool0−Qegrc2 (5)
The flow rate reduction allowance Qegrc2 in the region R2 is calculated, for example, by searching a table having the characteristics shown in FIG. 19 from the external EGR rate Pegr.
[0089]
As shown in FIG. 19, the flow rate reduction allowance Qegrc2 is a value that decreases as the external EGR rate Pegr decreases. This flow rate reduction allowance is to prevent the external EGR gas from being overcooled by reducing the flow rate of the cooling water flowing to the EGR cooler 55 when the external EGR rate is reduced because the reduction flag = 1. .
[0090]
The external EGR rate Pegr when the reduction flag = 1 is equal to PegrTR during the transition as described above with reference to FIGS. 12 and 13, and becomes P′egr2 after the transition. PegrTR representing the external EGR rate during the transition becomes smaller from Pegr0 to P'egr2. Accordingly, when PegrTR representing the external EGR rate during the transition is reduced from Pegr0 to P'egr2, the cooling water flow rate is reduced by the flow rate reduction allowance Qegrc2 according to FIG.
[0091]
Steps 79 to 81 that are processing in the region R3 are the same as steps 76 to 78 that are processing in the region R2. In other words, if “2” in steps 76 to 78 is replaced with “3”, the operations in steps 79 to 81 are obtained. In step 80, a flow rate reduction margin Qegrc3 in the region R3 is calculated by searching a table having the characteristics of the broken line in FIG. 19 from the external EGR rate Pegr. The flow rate reduction allowance Qegrc3 in the region R3 is smaller than the flow rate reduction allowance Qegrc2 in the region R2 with respect to the external EGR rate Pegr having the same value (see FIG. 19).
[0092]
The flow rate control valve 56 is controlled so that the cooling water flow rate Qcool determined in this way flows.
[0093]
The above-described flow is shown in a simplified manner. That is, when there is an operation condition in the region R2, the external EGR rate is changed from the basic value Pegr0 to the external EGR rate P'egr2 after the target reduction because the reduction flag is set to 1, and represents the external EGR rate during the transition The reduction flag = 0 at the timing when PegrTR coincides with the target EGR rate P′egr2 after the target reduction. However, after the reduction flag = 1 and before the reduction flag = 0, the driving condition is out of the region R2. Is also possible. However, the above flow is not created including this case.
[0094]
Further, once the control shown in FIG. 4 is performed in the region R2, the control shown in FIG. 4 is not repeatedly performed for the second time and the third time as long as the control remains in the same region R2. After the control shown in FIG. 4 is once performed in the region R2, when the operating condition changes to leave the region R2 and return to the region R2, the control shown in FIG. 4 is performed once again.
[0095]
4 and 5 show a case where the amount of heat received by the resin intake part simply increases. However, the resin intake part not only receives heat from the external EGR gas, but also depends on the operating conditions. Since heat may be released to the gas, the amount of heat received by the resin intake parts actually increases or decreases. Since the amount of heat released from the resin intake component can also be estimated according to the operating conditions, this case is not excluded from the present invention.
[0096]
Here, the operation of the present embodiment will be described.
[0097]
In the region R1, since heat damage to the resin intake component due to the EGR gas temperature does not matter, the EGR valve 26 is opened to introduce the external EGR gas into the resin intake component. At this time, the EGR cooler 55 is not operated, and the external EGR rate is increased to the external EGR rate basic value Pegr0 determined from the demand for combustion stability, and thereby the fuel efficiency improvement effect can be maximized.
[0098]
In the region R2, since the external EGR gas temperature is relatively high such as 130 to 170 ° C., if the resin intake component is exposed to the external EGR gas at this temperature for a long time, the resin intake component is thermally damaged. There is a risk of inviting. In this region R2, external EGR gas is introduced, but when the amount of heat received Smheat of the resin intake part determined by the engine controller 31 reaches a threshold value X determined from the thermal demand of the resin intake part. Then, the external EGR rate is decreased until the EGR rate (P′egr2) determined from the requirements of a temperature at which there is no problem with thermal damage of the resin intake parts and a temperature at which combustion stability can be ensured. At this time, the operation of the EGR cooler 55 causes a decrease in gas temperature and deteriorates combustion stability. Therefore, the cooling water flow rate is controlled to the minimum necessary. In parallel, the VTC mechanism 29 is controlled to increase the valve overlap amount of the intake and exhaust valves and increase the share ratio of the internal EGR rate, thereby reducing the fuel efficiency improvement effect due to the decrease in the external EGR rate. Can be supplemented.
[0099]
The action in the region R3 is the same as the action in the region R2. That is, in the region R3, the resin intake parts are exposed to high-temperature EGR gas exceeding 170 ° C., which causes thermal damage. Therefore, similarly to the region R2, the external EGR rate is determined by the heat of the resin intake components. The temperature is reduced until the EGR rate (P'egr3) determined from the requirements of a temperature at which there is no problem with thermal damage and a temperature at which combustion stability can be ensured. Also at this time, the operation of the EGR cooler 55 causes a decrease in gas temperature and deteriorates the combustion stability. Therefore, the cooling water flow rate is controlled to the minimum necessary. In parallel, the VTC mechanism 29 is controlled, the valve overlap amount is increased, and the share ratio of the internal EGR rate is further increased with respect to the region R2, thereby reducing the fuel efficiency effect due to the decrease of the external EGR rate. Can be supplemented.
[0100]
Here, the EGR valve 26 as an external EGR device and the VTC mechanism 29 as an internal EGR device are used in combination, and the share of the external EGR rate is decreased and the share of the internal EGR rate is increased as the load becomes higher. The sex will be explained. Conversely, relying solely on the EGR valve 26 and the EGR cooler 55 raises the following two concerns.
[0101]
The first concern is that even if high temperature external EGR gas at high load is introduced into the resin intake component, there is a limit due to the heat resistance requirement of the resin intake component. For example, when an external EGR gas at 150 ° C. is directly introduced into the resin intake collector 2, the surface directly exposed to the external EGR gas causes melting. For example, when external EGR gas at 130 ° C. is introduced, melting damage does not occur immediately, but thermal fatigue accumulates by operating in the same region for a long time, and melting damage occurs. There is a fear.
[0102]
Another concern is that when an external EGR device is used, the cooling of the external EGR gas by the operation of the EGR cooler 55 decreases the combustion speed even at high loads, and has a large adverse effect on the combustion stability. is there. At this time, a restriction is imposed on the external EGR rate in terms of combustion stability, and as a result, the fuel efficiency effect due to the introduction of the external EGR gas is reduced.
[0103]
On the other hand, by reducing the share ratio of the external EGR rate and increasing the share ratio of the internal EGR rate, it becomes possible to solve the above-mentioned two issues at the same time.
[0104]
As described above, in the present embodiment (the invention described in claims 3 and 4), the area where the external EGR gas is introduced is expanded, and the external EGR rate (external EGR ratio basic value Pegr0) in that area is also increased. Then, by controlling the EGR valve opening so that the external EGR rate basic value Pegr0 is obtained, the fuel efficiency is greatly improved by EGR, while the external EGR rate basic value Pegr0 and the intake air flow rate QA are used to obtain the external EGR rate. The gas flow rate Qegr is calculated, and the heat receiving amount Smheat of the resin intake component is calculated from the external EGR gas flow rate Qegr and the EGR gas temperature Tegr, and the heat receiving amount Smheat of the resin intake component is equal to or greater than the threshold value X. Sometimes the external EGR rate is decreased, the internal EGR rate is increased, and the flow rate of cooling water flowing to the EGR cooler does not deteriorate the combustion stability By reducing to a level, the temperature of the external EGR gas to be introduced into the resin intake part is appropriately maintained.
[0105]
As a result, it is possible to ensure the combustion stability while satisfying the heat resistance requirements of the resin intake parts, and to maintain the fuel efficiency improvement effect by EGR.
[0106]
In the embodiment, the case of resin as a material other than metal has been described. However, the present invention is not limited to this, and the present invention can be applied to any material that is thermally damaged by high-temperature external EGR gas.
[0107]
In the embodiment, the sharing ratio between the external EGR rate and the internal EGR rate is variably controlled. However, the sharing ratio between the external EGR gas amount and the internal EGR gas amount may be variably controlled.
[0108]
Not limited to the embodiment, the sharing ratio between the external EGR rate (or external EGR gas amount) and the internal EGR rate (or internal EGR gas amount) is changed according to the engine load state, and the external EGR rate is shared as the load becomes higher. The ratio may be decreased and the share ratio of the internal EGR rate may be increased (the invention according to claim 1).
[Brief description of the drawings]
FIG. 1 is a system schematic diagram of an embodiment.
FIG. 2 is a cooling water flow diagram.
FIG. 3 is an operation region diagram.
FIG. 4 is a waveform diagram showing changes in an external EGR rate and an internal EGR rate in a region R2.
FIG. 5 is a waveform diagram showing changes in an external EGR rate and an internal EGR rate in a region R3.
FIG. 6 is a flowchart for explaining setting of a reduction flag.
FIG. 7 is a flowchart for explaining calculation of a heat reception amount of a resin intake part.
FIG. 8 is a characteristic diagram of a basic value of an external EGR rate.
FIG. 9 is a characteristic diagram of exhaust temperature.
FIG. 10 is a characteristic diagram of a basic value of the cooling water flow rate.
FIG. 11 is a characteristic diagram of a temperature reduction allowance.
FIG. 12 is a flowchart for explaining determination of an external EGR rate.
FIG. 13 is a flowchart for explaining determination of an external EGR rate.
FIG. 14 is a characteristic diagram of an external EGR rate after target reduction.
FIG. 15 is a flowchart for explaining determination of a target internal EGR rate and a target cam phase.
FIG. 16 is a characteristic diagram of a target internal EGR rate.
FIG. 17 is a characteristic diagram of a target cam phase.
FIG. 18 is a flowchart for explaining determination of an EGR cooler cooling water flow rate.
FIG. 19 is a characteristic diagram of a flow rate reduction allowance.
[Explanation of symbols]
22 Fuel injector
25 EGR passage
26 EGR valve (external EGR device)
29 VTC mechanism (internal EGR device)
31 Engine controller
55 EGR cooler (external EGR gas cooling system)
56 Flow control valve

Claims (6)

In an engine in which air is introduced into a combustion chamber through an intake part formed of a resin consisting of an intake collector and an intake manifold ,
An EGR passage communicating with the exhaust manifold and the intake manifold, an EGR valve capable of adjusting the amount of exhaust gas flowing to the intake manifold via the EGR passage, and an actuator for driving the EGR valve, or an external EGR rate or an external An external EGR device capable of adjusting the amount of EGR gas;
An internal EGR device capable of adjusting an internal EGR rate or an internal EGR gas amount;
Of the EGR region into which the external EGR gas is introduced, the external EGR rate or the external EGR gas depending on the engine load state in the region that may cause thermal damage to the resin intake parts and the region that causes thermal damage to the resin intake parts The share ratio between the amount and the internal EGR rate or the internal EGR gas amount is changed, and the share ratio of the external EGR rate or the external EGR gas amount is decreased as the load becomes higher, and the internal EGR rate or the internal EGR gas amount is shared. An engine exhaust gas recirculation control device comprising: a share ratio control means for increasing the ratio. An external EGR gas cooling device that cools the external EGR gas by performing heat exchange between the external EGR gas and the refrigerant;
The refrigerant flow rate that flows through the external EGR gas cooling device is reduced to a flow rate that does not deteriorate combustion stability when the external EGR rate or the share ratio of the external EGR gas amount is reduced as the load increases. Item 2. An exhaust gas recirculation control device for an engine according to Item 1. In an engine in which air is introduced into a combustion chamber via an intake part formed of resin,
An external EGR device capable of adjusting an external EGR rate or an external EGR gas amount;
An internal EGR device capable of adjusting an internal EGR rate or an internal EGR gas amount;
The share ratio between the external EGR rate or external EGR gas amount and the internal EGR rate or internal EGR gas amount is changed according to the engine load state, and the share ratio of the external EGR rate or external EGR gas amount is increased as the load becomes higher. A share ratio control means for decreasing and increasing the share ratio of the internal EGR rate or the internal EGR gas amount;
A thermal history estimating means for estimating a thermal history of the intake air component by external EGR gas ;
With
The reason why the share ratio of the external EGR rate or the external EGR gas amount is decreased and the share ratio of the internal EGR rate or the internal EGR gas amount is increased is that the heat history by the external EGR gas with respect to the estimated intake component is heat resistant. exhaust gas recirculation control device features and to Rue engine that is when it becomes more than a threshold determined by the limit. An external EGR gas cooling device that cools the external EGR gas by performing heat exchange between the external EGR gas and the refrigerant;
The external EGR gas is cooled by the external EGR gas cooling device before the thermal history of the estimated intake air component by the external EGR gas exceeds a threshold value determined by a heat resistance limit,
4. The engine flow rate according to claim 3, wherein when the external EGR rate or the share ratio of the external EGR gas amount is reduced, the flow rate of the refrigerant flowing through the external EGR gas cooling device is reduced to a flow rate at which combustion stability does not deteriorate. Exhaust gas recirculation control device.   The engine exhaust gas recirculation control apparatus according to claim 3, wherein the heat history is a heat receiving amount of the intake component from an external EGR gas.   6. The engine exhaust gas recirculation control apparatus according to claim 5, wherein the heat reception amount is estimated based on an engine load, a rotation speed, and an intake air amount.

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