JP2002188523A - Control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an engine which can suppress discharge of unburned fuel. SOLUTION: In an engine, having a means performing EGR introducing exhaust gas to a combustion chamber and a means installed in an exhaust pipe to convert HC which is unburned fuel, the means converting HC performs EGR during the time from an engine start to having converting capacity (ON).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an engine control device, and more particularly to an engine control device for controlling EGR (exhaust gas recirculation) for guiding exhaust gas to a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, as a method of controlling fuel injection of an in-cylinder fuel injection type engine, for example, Japanese Unexamined Patent Publication No.
A technique disclosed in Japanese Patent Application Laid-Open No. 0907 is known. This is to open the EGR passage at the start of the engine, guide the exhaust gas including the injected fuel from the exhaust passage to the intake passage,
The unburned air-fuel mixture at the time of starting is supplied again to the combustion chamber to promote combustion and prevent unburned fuel from being discharged to the outside.

[0003]

However, such an engine control device disclosed in the prior art is intended to recirculate the fuel discharged as it is in a state in which normal combustion cannot occur at the time of starting to the intake system. In the case where combustion occurs but the exhaust contains a large amount of unburned fuel after the engine is started, no consideration is given to the discharge of unburned fuel to the outside. May not be sufficient.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to provide an engine control device capable of suppressing discharge of unburned fuel.

[0005]

In order to achieve the above object,
The control device for the engine according to the present invention uses the EG during the period when the means for converting HC has the ability to convert from starting the engine.
R is performed.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a control system for a direct injection engine according to the present invention.

FIG. 3 is an overall configuration diagram of the in-cylinder injection engine system which is a feature of the present embodiment. The flow rate of air taken into the engine 1 is controlled by an electronically controlled throttle valve, that is, an ETC 4.

In FIG. 3, air taken into the engine 1 is taken in from an intake port 6 of an air cleaner 5, and an air flow meter 7 is a means for measuring an intake air amount Qa.
And enter the collector 8. The air taken into the collector 8 is distributed to each intake pipe 10 connected to each cylinder 9 of the engine 1, and is guided into the combustion chamber of the cylinder 9.

On the other hand, fuel such as gasoline is sucked and pressurized from a fuel tank 11 by a fuel pump 12 and supplied to a fuel system in which an injector 13 is provided. The pressurized fuel is regulated to a constant pressure (for example, 5 MPa) by the fuel pressure regulator 14, and each cylinder 9
The fuel is injected into the cylinder 9 from an injector 13 provided in the cylinder 9. The injected fuel is ignited by an ignition plug 16 in response to an ignition signal whose voltage is increased by an ignition coil 15.

A signal indicating the intake air flow from the air flow meter 7 and an angle signal PO of a crankshaft 19 from a crank angle sensor 18 are sent to the control unit 17.
S and an exhaust gas detection signal from an A / F sensor 22 provided in front of the catalyst 21 in the exhaust pipe 20 are input.

The intake air amount signal detected by the air flow meter 7 is processed by a filter processing means or the like to be converted into an air amount. After that, the intake air amount is divided by the engine speed to obtain an air-fuel ratio of stoichiometric (A). /F=14.7) to obtain a basic fuel injection pulse width per cylinder, that is, a basic fuel injection amount. Thereafter, based on the basic fuel injection amount, various fuel amount corrections are performed in accordance with the operating state of the engine to obtain the fuel injection amount, and then the injector is driven to supply fuel to each cylinder. Also, the exhaust pipe 20
Since the actual air-fuel ratio of the exhaust gas can be known from the output of the A / F sensor 22 provided in the controller, when it is desired to obtain a desired air-fuel ratio, the closed-loop control for adjusting the supplied fuel amount by the signal of the A / F sensor , A desired air-fuel ratio state can be obtained.

Next, the control unit 17 and the sensors and actuators connected thereto will be described with reference to FIG. The electric signal from each sensor is input to the calculating means 123 in the control unit 17, and the calculating means 123 recognizes the state of the engine and its surroundings based on the signal. According to the recognized state, a calculation process is appropriately performed to output a command signal for driving the actuator. FIG. 9 shows a command signal for the injection valve or injector and the ignition coil as a representative example. The command signal is electrically H for both the injection valve and the ignition coil.
Signals representing I and LO.
The signal is amplified by 6 into a signal having electric energy sufficient for driving the actuator, and supplied to the injection valve 125 and the ignition coil 127.

[0013] The injection valve 125 is energized to the internal coil during the HI signal, and injects fuel by opening the fuel metering section. While the fuel metering unit is open, fuel is injected at a predetermined flow rate per unit time by the fuel pressure on the upstream side,
Therefore, the fuel supply amount is controlled by controlling the valve opening time. The ignition coil 127 is energized to the internal primary coil during the HI signal, and generates an induced current in the 2 o'clock side coil simultaneously with the end of the HI signal, thereby generating a discharge in the ignition plug and igniting the air-fuel mixture.

Here, the cylinder 9 is provided with the injector 1
Since the fuel is supplied directly from 3, the fuel injection timing for combustion is limited during the intake stroke or the compression stroke. FIG. 16 shows an example of the timing in the case of performing the fuel injection in the intake stroke, and FIG. 6 shows an example of the timing in the case of performing the fuel injection in the compression stroke. In any case, the ignition timing is in the latter half of the compression stroke when the air-fuel mixture is compressed and easily ignited. The combustion behavior by the fuel injection in the intake stroke and the compression stroke has the following differences, and each has its own advantages and disadvantages. Therefore, it is efficient in engine operation to properly use both depending on the operation state of the engine. FIG. 15 shows an example of the control of the proper use. In block 161, the engine speed, the torque to be output by the engine,
It is determined whether stratified combustion or homogeneous combustion is to be performed based on engine operating conditions such as the cooling water temperature of the engine. Stratification,
As will be described later, homogeneous combustion represents the degree of dispersion of the air-fuel mixture inside the combustion chamber, which can be controlled by the fuel injection timing. Stratification,
For the homogeneous combustion determination, a fine-grained determination can be made by appropriately inputting an information source appropriate for properly using the two in addition to the illustrated signal.

Next, the determination results of stratification and homogeneity are passed to blocks 162 and 163, respectively. In block 162, a fuel injection timing suitable for performing stratified combustion or homogeneous combustion is calculated. In block 163, stratified combustion or homogeneous combustion is calculated. An ignition timing suitable for performing homogeneous combustion is calculated.

The behavior of such an engine in which fuel is injected and burned during the compression stroke will be described with reference to FIG. (A), (B), and (C) of the figure show the state of the combustion chamber during the compression stroke in a time-series manner, in which the injection of the fuel xx from the injector 13 is completed in (A). At (B), the piston has risen from (A), and the fuel xx reaches the crown surface of the piston. The piston is provided with a concave portion for preventing diffusion of the fuel and for transporting the fuel upward. Therefore, when reaching (C), the fuel xx is accumulated in the vicinity of the spark plug in a form that is appropriately mixed with air. If ignition is performed at this point, a mixture having an appropriate air-fuel ratio near the spark plug can be ignited, and good combustion can be obtained.

At this time, since no fuel exists in the combustion chamber other than the vicinity of the ignition plug, the air-fuel ratio is large and lean in the entire combustion chamber, and the pumping loss of the engine can be reduced in such combustion. Thus, better fuel economy can be obtained by burning a homogeneous mixture.

The sensitivity of the combustion to the temperature of the engine will be described with reference to FIG. The temperature of the engine is generally represented by the temperature of the cooling water. In the range where the engine water temperature is high, the injected fuel is vaporized in the combustion chamber, so that the concentration of HC, which is unburned fuel in the exhaust gas, is low. When the engine water temperature falls below a predetermined range, the fuel does not reach the vaporization temperature, and the HC concentration rapidly increases. Therefore, at temperatures other than extremely low temperatures, the engine can be operated by stratified combustion without significantly affecting combustion.

Here, E for reducing exhaust gas to intake air
Consider adding GR during stratified operation. EGR
Is connected to the exhaust pipe 20 by the EGR valve 21 shown in FIG.
By controlling the opening area of the passage that communicates with the collector 8, a desired amount of exhaust gas is guided into the intake pipe by the pressure difference between the collector 8 and the exhaust pipe 20 and supplied to the combustion chamber. Since EGR gas is gas after combustion,
When re-inhaled into the combustion chamber, it generally acts as a factor inhibiting combustion. FIG. 11 shows an example of the effect of EGR on engine performance. The condition of the air-fuel ratio in FIG. 11 is that the stoichiometric air-fuel ratio is constant, and the next fuel injection is the intake stroke injection described later. Since the nitrogen oxides NOx in the exhaust gas components are generated when the combustion temperature is high, if the combustion is hindered by the EGR gas, the emission amount will decrease. Therefore, as shown in FIG. 11, the relationship between the EGR rate, which is the ratio of the air taken into Kinki and the EGR gas, and the NOx concentration discharged from the engine is such that the NOx concentration decreases as the EGR rate increases. Become. On the other hand, the stability of combustion deteriorates as the EGR rate increases because combustion is inhibited.

However, in stratified operation, the EGR gas contains oxygen because the air-fuel ratio is lean. Thereby, EGR
The influence of gas combustion inhibition is reduced, and combustion is not impaired even at a high EGR rate. That is, even if the ratio of the intake air and the EGR gas of the gas supplied to the combustion chamber changes, the influence on the combustion stability is small. FIG. 4 shows an example of the characteristic. The horizontal axis in the figure is A / F, which is the ratio between the intake air amount and the supplied fuel, and the vertical axis is the EGR rate, which is the ratio between the new intake air amount and the EGR gas. AA in the figure indicates a range where the combustion stability satisfies a certain reference value, and the upper right side thereof is on a line in which the amounts of the EGR gas and the new intake air are substantially equal in total, and on this line, the combustion chamber Although the ratio between the intake air of the gas to be inhaled and the EGR gas is changed, it indicates that the influence on the combustion stability is constant. The same applies to the lower left side. The difference between the two is that the oxygen concentration in the EGR gas is low when the A / F is rich.

FIG. 5 shows the NOx concentration in the exhaust gas at this time.
Shown in Although the air-fuel ratio is lean, since the EGR gas contains nitrogen N ₂ and carbon dioxide CO ₂ which are inhibitors of combustion, the temperature during combustion decreases as the EGR rate increases, and as a result, the NOx concentration decreases. descend.

As described above, in stratified combustion, a high E
Good combustion stability can be obtained even if EGR is added at the GR rate.

On the other hand, although not shown, when fuel is injected during the intake stroke, air is sucked from the intake valve as the piston descends, and the injected fuel rides on the intake air and enters the combustion chamber uniformly. Spread. Thereafter, the process proceeds to the compression stroke, and the air-fuel mixture is compressed and ignited in the form of a homogeneous mixture of air and fuel. In this case, good combustion can be obtained by setting the air-fuel ratio to be richer than in the case of fuel injection in the above-described compression stroke.

On the other hand, when the engine is stopped, the temperature of the catalyst 21 is equal to the ambient temperature, and the temperature of the catalyst 21 is increased by the heat of the exhaust gas after the engine is started. Further, the catalyst has a function of oxidizing and reducing the reducing agent and the oxidizing agent in the exhaust gas, respectively, and discharges the same. The oxidizing and reducing ability is, for example, as shown in FIG. Indicates a high value.

However, immediately after the start of the engine, the temperature of the entire engine including the exhaust pipe as well as the catalyst is substantially equal to the temperature as described above. Therefore, there is not enough temperature in the exhaust pipe to complete the reaction. FIG. 13 shows the amount of HC emission from the engine immediately after the start and the amount of HC emission after the catalyst. AA in the figure is the HC emission from the engine, and BB is the HC emission after the catalyst. Immediately after start-up when the temperature of the catalyst is low, the amount of HC emission from the engine and the amount of HC emission after the catalyst are almost equal because the catalyst has not been activated. The catalyst is activated and H
HC from the engine to exert the effect of oxidizing C
The HC emission after the catalyst is lower than the emission. In addition, the amount of HC emission from the engine slightly decreases as the engine warms up.

Therefore, circulating the exhaust gas having a relatively high HC concentration immediately after the start to the intake side to temporarily accumulate it is effective in reducing the amount of HC discharged from the exhaust pipe. That is, immediately after the start, EGR is added, and exhaust gas having a high HC concentration is accumulated in the EGR pipe. HC in EGR gas that recirculates and is sucked into the engine together with fresh air
However, while the temperature of the exhaust pipe is low, the exhaust gas discharged from the engine is not much different from the HC concentration without EGR addition. However, EGR
Since the exhaust gas filled in the pipe is not exhausted from the engine, H contained in the exhaust gas corresponding to the EGR pipe capacity is used.
C is not emitted from the engine.

FIG. 1 shows one embodiment. When the EGR is turned on immediately after the start, the exhaust gas discharged from the exhaust pipe flows to the EGR pipe when the EGR is off, so that the amount of HC discharged after the catalyst is lower than the amount of HC discharged from the engine. After that, after the temperature of the catalyst reaches the predetermined temperature, the behavior becomes the same as the behavior described with reference to FIG. 13, and it is not necessary to add the EGR for this purpose. At this time, although the addition of EGR is stopped in FIG. 1, stop and continuation may be selected for another purpose of adding EGR.

The behavior of EGR gas and intake air during EGR addition will be described with reference to FIG. In FIG. 7, AA is an engine, BB is an intake pipe, and CC is an exhaust pipe. A portion indicated by a broken line in the drawing is a portion where the EGR gas exists, and the EGR gas circulates during this portion during the EGR addition. In the steady state, the amount of air consumed by the engine and the amount of fuel consumed are equal to the amount released as exhaust gas.
It can be considered that the GR gas circulates and stays stagnant. Also, its component is equal to exhaust gas. That is, when the EGR is ON, the exhaust gas can be stored in the capacity indicated by the broken line. Therefore, HC contained in the exhaust gas can be accumulated, and if this is released after the catalyst is activated, the HC is oxidized by the catalyst and is not released to the outside.

Here, the addition of EGR for this purpose is different from the generally used reduction of NOx emission and improvement of fuel efficiency by reduction of intake resistance. Therefore, for example, when the EGR is added after the engine is warmed up, and when the supplied air-fuel ratio, EG
It is better to give the R rate differently and measure the target reduction of HC emission. If the A / F is set to be rich as shown in FIG. 4, the EGR can be added at a large EGR rate. Therefore, it is preferable to operate at an A / F that enables a large EGR rate and to operate at a high EGR rate. good.

Another consideration is the amount of HC exhausted from the engine. The A / F and EGR rates are determined in consideration of the two in order to reduce the HC emission of the engine in addition to the above. Is good.

FIG. 10 shows an example of a process for executing such control.
Shown in First, at step 241, it is determined whether the engine water temperature is within a predetermined range. If the engine water temperature is low, stratified charge combustion cannot be performed. If the engine water temperature is high, the engine is warmed up and the catalyst can be determined to be activated. Proceed to. Further, as another method for determining that the engine and the catalyst are in a warmed-up state, whether a predetermined time has elapsed since the engine was started may be used, or both conditions may be used. More specifically, it is conceivable that the condition is a total fuel consumption amount after starting. Also, since the catalyst warm-up process is heat exchange from exhaust gas, the catalyst temperature is estimated by estimating the heat exchange state from various input conditions and output signals required for engine control, and the catalyst is warmed up. A method of determining that the operation has been performed is also possible. More directly, make a sensor to measure the temperature of the catalyst,
The determination may be made based on the measurement result.

The specific conditions under which the catalyst is brought into a warm-up state are simply a state close to 100% of complete warm-up. However, when the activation of the catalyst can be promoted by, for example, retarding the ignition timing, which is made possible by not adding the EGR, the addition of the EGR may be terminated, and the control may be switched to the retarding operation of the ignition timing. Can be FIG. 20 shows a control flow in that case.

If it is within the predetermined range, the flow ends without performing the processing according to the present embodiment. Step 2
At 42, it is determined whether the EGR can be added, that is, whether the engine has just been started. Before the start of the engine, the pressure difference between the intake pipe and the exhaust pipe is small, and a sufficient EGR amount cannot be obtained.

In the next step 243, since it has been determined that the EGR can be added, it is determined that the stratified combustion to withstand the high EGR rate is performed. This processing is a part of step 161 in FIG. Then step 2
At 44, a target EGR rate according to the operating state of the engine is calculated and commanded. As described with reference to FIG. 4, when the target EGR rate is increased within a range where combustion is stable together with the target A / F, the amount of exhaust gas that can be accumulated can be increased.

The following is conceivable as the timing for stopping the addition of EGR not depending on the purifying ability of the catalyst.

As described in the description of FIG. 7, since the exhaust gas containing HC is stored in the portion shown by the broken line in FIG. 7, the higher the HC concentration of the exhaust gas in this portion is, the larger the amount of HC is.
Can be stored. On the other hand, when the HC concentration of the exhaust gas discharged from the engine decreases as time passes after the start, the exhaust gas having a high HC concentration before the HC concentration decreases is stored in the EGR passage. More HC can be stored. In such a case, when the HC concentration of the engine decreases immediately after the start, EG
If the addition of R is stopped, the EGR is added again after the catalyst is activated, and the HC in the EGR passage is purged, the amount of HC discharged after the catalyst can be reduced.

Since the specific conditions for determining a decrease in HC depend on the state of fire spread of the engine, it can be estimated by parameters necessary for engine control, such as the time after starting and the engine water temperature. It may be detected by a sensor for measuring the concentration of the particles.

FIG. 21 shows an example of the behavior after starting according to the embodiment of the present invention. HC AA of exhaust gas from engine
Decrease over time, and the HC discharge amount BB discharged from the exhaust pipe is reduced by adding EGR at the initial stage. The behavior after the catalyst temperature has risen is the same as the behavior described in FIG.

Further, in the piping for recirculating EGR, HC
By installing a substance having a function of adsorbing HC, the amount of HC emission can be reduced. FIG. 12 shows the configuration. As in FIG.
AA is an engine, BB is an intake pipe, and CC is an exhaust pipe.
DD is an EGR valve which is located in an EGR passage communicating from the exhaust pipe to the intake pipe, and which can adjust the amount of EGR by controlling the opening area. EE is a substance having a function of adsorbing HC.

FIG. 14 shows an example of characteristics of a substance having a function of adsorbing HC. When the temperature of the substance is low, a large amount of HC is adsorbed, and when the temperature is high, the amount of adsorbed HC is reduced. Therefore, when the temperature of the substance changes from a low temperature to a high temperature, it has a characteristic of desorbing HC once adsorbed.

When the EGR control shown in FIG. 1 is performed, the exhaust gas, that is, the EGR gas is recirculated from the CC to the BB in FIG.
C is adsorbed by the EE and is not newly sucked into the combustion chamber. Therefore, the HC adsorbed on the EE is not discharged from the exhaust pipe. Further, the temperature of the EE is gradually increased by the heat of the exhaust gas, and HC is desorbed as described with reference to FIG. The desorbed HC is supplied to the combustion chamber, a part of the HC is burned, and a part of the HC is discharged to the exhaust pipe. No HC is emitted. Therefore, the amount of HC emission from the start becomes a behavior as shown in FIG. 18, and the amount of HC emission can be made smaller than the behavior described in FIG.

Further, as shown in FIG.
If there is a device such as FF that can control the exhaust pipe opening area downstream of the GR branch, the degree of freedom in controlling the EGR amount is higher than when only the EGR valve DD exists. Therefore, the amount and rate of EGR that can be recirculated can be controlled in a wide range, which is effective in applying the present invention.

In the above description, an example of application to an engine in which fuel is injected into the combustion chamber has been described. However, the present invention is not limited only to the application to an external engine. The present invention is also applicable to an engine that injects fuel into the engine.

Although some embodiments of the engine control device according to the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but includes the spirit of the invention described in the claims. Various changes can be made in the design without departing from the scope of the invention.

[0045]

As will be understood from the above description, the engine control device of the present invention can provide an engine control device capable of suppressing the discharge of unburned fuel.

[Brief description of the drawings]

FIG. 1 is a view for explaining the operation of one embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of an engine to which the present invention is applied.

FIG. 3 is a diagram showing an overall configuration of an engine to which the present invention is applied.

FIG. 4 is a diagram illustrating characteristics of the operation of the engine.

FIG. 5 is a diagram illustrating characteristics of the operation of the engine.

FIG. 6 is a diagram illustrating characteristics of the operation of the engine.

FIG. 7 is a view for explaining the principle of one embodiment of the present invention.

FIG. 8 is a diagram illustrating characteristics of the operation of the engine.

FIG. 9 is a diagram illustrating a control device to which the present invention is applied.

FIG. 10 is a diagram for explaining the operation of one embodiment of the present invention.

FIG. 11 is a diagram illustrating characteristics of the operation of the engine.

FIG. 12 is a diagram illustrating a configuration of one embodiment of the present invention.

FIG. 13 is a diagram illustrating characteristics of the operation of the engine.

FIG. 14 is a diagram illustrating characteristics of one embodiment of the present invention.

FIG. 15 is a diagram illustrating a control device to which the present invention is applied.

FIG. 16 is a diagram illustrating the operation of the engine.

FIG. 17 is a diagram illustrating characteristics of an engine to which the present invention is applied.

FIG. 18 is a view for explaining the operation of one embodiment of the present invention.

FIG. 19 is a view for explaining the configuration of one embodiment of the present invention.

FIG. 20 is a view for explaining the operation of one embodiment of the present invention.

FIG. 21 is a view for explaining the operation of one embodiment of the present invention.

[Explanation of symbols]

1 ... engine body, 4 ... ETC, 5 ... air cleaner, 6
… Inlet, 7… air flow meter, 8… collector, 9…
Cylinder, 10 ... intake pipe, 11 ... fuel tank, 12 ... fuel pump, 13 ... injector, 14 ... fuel pressure regulator, 15 ... ignition coil, 16 ... ignition plug, 17 ... control unit, 18 ... crank angle sensor, 19 ... crank Shaft, 20 ... exhaust pipe, 21 ... EGR valve, 22 ...
A / F sensor, 23 ... catalyst, 24 ... A / F sensor, 25
... Precatalyst.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 21/08 301 F02D 21/08 301C 43/00 301 43/00 301N 301J 45/00 312 45/00 312B (72) Inventor Yoshiyuki Yoshida 2520 Oita, Hitachinaka-shi, Ibaraki F-term in the Automotive Equipment Group of Hitachi, Ltd. FA27 3G091 AA11 AA17 AA23 AA24 AA28 AB02 BA03 BA15 BA32. FA18 GA01 GA02 HB01Z HB02X HD02Z HD07X HE08Z

Claims (4)

[Claims] In an engine control apparatus having means for performing EGR for guiding exhaust gas to a combustion chamber and means for converting HC, which is unburned fuel, provided in an exhaust pipe, the means for converting HC starts from engine start. An engine control device for performing EGR until the engine has a conversion capability. 2. The engine control device according to claim 1, wherein a substance that adsorbs HC is provided in the EGR passage. 3. The control system for a direct injection engine according to claim 1, wherein the engine injects fuel into the combustion chamber, and performs fuel injection in a compression stroke while EGR is applied. 4. An engine control device comprising: means for performing EGR for guiding exhaust gas to a combustion chamber; and means for converting HC which is unburned fuel, provided in an exhaust pipe.
A control device for a direct injection type engine, wherein the addition of EGR is stopped when the concentration of HC discharged from the engine becomes low after adding R.