JP2006299816A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a direct injection engine representing a high-accuracy concrete structure for suppressing intermittent combustion at the time of transferring to a stratified combustion operation immediately after starting. <P>SOLUTION: This control device for a direct injection engine executes EGR (exhaust gas recirculation) in the stratified combustion operation by changing over homogeneous combustion operation and stratified combustion operation according to an engine operating condition. In starting, the homogeneous combustion operation as a first warming up operation is performed until a cooling water temperature reaches a reference temperature. Stratified combustion operation as a second warming up operation is performed until a combustion chamber temperature reaches a target combustion chamber temperature from a point of time when the cooling water temperature reaches the reference temperature. The stratified combustion operation as a steady operation is executed consecutively when the combustion chamber temperature reaches the target combustion temperature. During the second warming up operation, the control device corrects to an EGR rate lower than an EGR rate at the time of the steady operation according to the combustion chamber temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an EGR control device for an internal combustion engine.

  When starting the engine, in order to warm up the engine body and catalyst quickly, perform homogeneous combustion operation to burn more fuel, and when the engine body and catalyst warm up, switch to stratified combustion operation to burn less fuel and fuel consumption There is a direct-injection gasoline engine that prevents the deterioration of the engine. The reason for warming the engine body and the catalyst quickly is to reduce friction loss and to activate the catalyst quickly. Homogeneous combustion refers to a method in which the entire combustion chamber is burned with the same air-fuel ratio (near the theoretical air-fuel ratio), and stratified combustion refers to a method in which a fuel rich layer (about the theoretical air-fuel ratio) and a thin layer are formed and burned To tell. In this type of engine, NOx is likely to be generated due to oxygen enrichment during stratified combustion operation. This NOx is occluded and reduced by a lean NOx catalyst, but the catalyst capacity is limited. Therefore, EGR (exhaust gas recirculation) is performed to introduce exhaust gas, which is an inert gas, into the combustion chamber, thereby reducing NOx generation. Suppressed.

However, if the EGR is performed at the same EGR rate as during steady operation (when warm-up operation is completed) at the time of transition to stratified combustion operation immediately after startup, the combustion chamber temperature has not risen to the temperature during steady operation. Combustion becomes unstable and smooth operation is hindered by intermittent combustion (so-called combustion fluctuation). By the way, intermittent combustion also deteriorates ride comfort. Further, since the combustion chamber temperature does not rise to the temperature during steady operation and NOx generation is small, it is not necessary to perform EGR at the same EGR rate as during steady operation.
For this reason, at the time of transition to the stratified combustion operation immediately after the start, it is desired to suppress intermittent combustion, that is, combustion fluctuation, by performing EGR less than the EGR rate during steady operation.

  In this connection, Patent Document 1 states in paragraph [0007] “After the start of the low-temperature internal combustion engine, an improved warm-up operation of the internal combustion engine is achieved. In the paragraph [0006], the stratified combustion operation can be controlled in relation to the temperature by the controller when the engine is cold. In paragraph [0009], "In a further advantageous variant of the invention ... the exhaust gas recirculation rate through the exhaust gas return guide valve is controlled in relation to the temperature" However, no further specific configuration is shown.

  Further, Patent Document 2 discloses an EGR control device characterized by means for varying the EGR correction amount according to the combustion method. However, this device reduces the EGR amount as the engine temperature of the internal combustion engine decreases. The EGR control device that corrects to the above is the base technology, and paragraph [0049] states that “the map calculation is performed on the EGR correction coefficient based on the coolant temperature (engine temperature)”. The purpose is to optimize the amount of EGR as a countermeasure against NOx and misfire.

  Also in Patent Document 3, an EGR control device having a similar configuration is disclosed, but the object is not countermeasures against intermittent combustion but NOx control in a transient state, which is different from the present invention. In addition, EGR control is performed based on the cylinder wall temperature. In paragraph [0017], “Cylinder wall temperature may be specified based on the output of a sensor that detects the cylinder wall temperature. It may only be estimated from correlated physical quantities. "

JP 2001-164966 A JP 2000-104627 A JP 2004-036557 A

  Conventionally, as described in Patent Document 2, the EGR correction at the time of shifting to the stratified charge combustion operation immediately after the start is performed according to the present invention “from the homogeneous combustion operation that is the first warm-up operation to the shift to the stratified combustion operation that is the second warm-up operation It was executed based on the same coolant temperature as the “switching standard”. (However, Patent Document 2 does not distinguish between the first warm-up operation and the second warm-up operation.)

The cooling water temperature on the basis of switching from the homogeneous combustion operation to the stratified combustion operation transition in the present invention is, for example, 80 ° C., and there is no particular problem.
However, when the cooling water temperature further rises, the thermostat disposed in the cooling water channel system opens, for example, at about 85 ° C., and the heated cooling water is cooled by the radiator. For this reason, when the water temperature increase rate curve converges, when the standard for switching from the second warm-up operation that requires EGR correction to the steady operation that does not require EGR correction is, for example, 90 ° C. at the water temperature, There was a problem that it was difficult to clearly match (at the time of zero EGR correction) and the actual transition to steady operation that does not require EGR correction, and the matching accuracy was very poor. In addition, when the automobile repeatedly accelerates or decelerates irregularly after the water temperature is converged, the water temperature is greatly disturbed, and there is a problem that becomes a disturbance factor of EGR correction.

  On the other hand, it is the combustion chamber temperature that directly affects engine combustion, and EGR correction should be performed based on the combustion chamber temperature. However, since it is difficult to measure the combustion chamber temperature, as described above, the correction is conventionally performed based on the water temperature. When the water temperature exceeds a water temperature (for example, 80 ° C.) that is a criterion for ending the first warm-up operation, the water temperature rise curve converges for the above-described reason. C)), it is difficult to determine the actual transition to steady operation, and the EGR correction is inaccurate.

  An object of the present invention is to provide a control device for a direct injection engine in which a specific configuration with high accuracy for suppressing intermittent combustion at the time of transition to a stratified combustion operation immediately after starting is shown.

According to the invention of claim 1,
A control device for a direct injection engine that switches between homogeneous combustion operation and stratified combustion operation according to the operating conditions of the engine, and executes EGR during stratified combustion operation,
At start-up, the homogeneous combustion operation as the first warm-up operation is performed until the cooling water temperature reaches the reference temperature, and from the time when the cooling water temperature reaches the reference temperature until the combustion chamber temperature reaches the target combustion chamber temperature. Stratified combustion operation as the second warm-up operation, and when the combustion chamber temperature reaches the target combustion chamber temperature, the stratified combustion operation as the steady operation is continuously executed,
During the second warm-up operation, there is provided a control device for a direct injection engine, wherein the EGR rate is corrected to be lower than the EGR rate during steady operation according to the combustion chamber temperature.

Thus, according to the control device of the first aspect, in the EGR control at the time of transition to the stratified combustion operation immediately after the start, the EGR rate is smaller than the EGR rate in the steady operation according to the combustion chamber temperature, not the cooling water temperature. By correcting to, intermittent combustion is suppressed. Thereby, a specific configuration is shown, and an accurate EGR rate correction control apparatus can be realized.
In addition, the reason for adopting the cooling water temperature instead of the combustion chamber temperature as the first warm-up operation end criterion is that the cooling water temperature can be easily measured and an accurate temperature value can be obtained up to about 100 ° C. This is because the cooling water temperature directly affects the engine friction loss. Incidentally, it is the lubricating oil temperature that has the most influence on the engine friction loss, but the accuracy is almost the same even if the coolant temperature is substituted.
The cooling water temperature has a higher rate of increase than the combustion chamber temperature. One of the reasons is that since the thermostat disposed in the cooling water channel system is closed at the time of starting, it is not cooled by the radiator.

According to invention of Claim 2,
The control device according to claim 1, wherein the combustion chamber temperature employs a piston surface temperature as a representative value.
Thus, according to the control device of the second aspect, since the piston surface temperature that most affects the combustion is set as the representative value of the combustion chamber temperature, the correction accuracy of the EGR rate is the best. During stratified combustion operation, fuel injection is performed near the compression top dead center, and fuel spray collides with the piston surface and burns, so the piston surface temperature has the most influence on combustion.

According to invention of Claim 3,
The control device according to claim 1 or 2, wherein the combustion chamber temperature is estimated as a sum of an initial combustion chamber temperature and a function of an integrated injection amount.
Thus, according to the control device of the third aspect, a rational and specific method for estimating the combustion chamber temperature is shown. The rate of increase of the combustion chamber temperature from the initial temperature is directly related to the integrated value of the amount of fuel injected and burned up to that point, and is determined by heat transfer and heat balance due to the combustion energy of the integrated value fuel. It is.

According to invention of Claim 4,
The control device according to claim 3, wherein the initial combustion chamber temperature employs the cooling water temperature or the lubricating oil temperature as a representative value.
Thus, according to the control device of the fourth aspect, a rational and specific method for estimating the initial combustion chamber temperature is shown. This is because the initial combustion chamber temperature is the same as the coolant temperature or the lubricating oil temperature when the engine is not started.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus of the direct injection type engine by which the specific structure with a sufficient precision which suppresses the intermittent combustion at the time of stratified combustion operation transfer immediately after a start was shown can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of a control device of the present invention and an engine controlled thereby. The engine 1 is configured as an in-line four-cylinder gasoline engine mounted on, for example, an automobile. Air (primary air) corresponding to the opening of the throttle valve 11 is sucked into the intake passage 7 of the engine 1 through an air filter, and the air is taken into each cylinder 3 through the intake passage 7. A fuel injection valve 12 and a spark plug 10 are provided in the cylinder 3.

  Exhaust gas generated by combustion in the cylinder 3 is guided to the catalyst 9 through the exhaust passage 8 and purified, and further purified by the catalyst 15, and then exhausted to the atmosphere through a silencer (not shown). The catalyst 9 is a well-known three-way catalyst that oxidizes HC and CO while reducing NOx. The catalyst 15 is a lean NOx catalyst that occludes and reduces NOx generated during the stratified combustion operation. Connected to the exhaust passage 8 is an EGR passage 13 for returning the exhaust gas that has passed through the catalyst 9 to the intake passage 7. The flow rate of the exhaust gas passing through the EGR passage 13 is controlled by the EGR valve 14.

  An air flow meter 21 that outputs a signal corresponding to the intake air flow rate, an intake air temperature sensor 22 that outputs a signal corresponding to the intake air temperature, and a throttle opening sensor that outputs a signal corresponding to the opening of the throttle valve 11 are provided in the intake passage 7. Are provided. The output signal of each sensor is led to an engine control unit (ECU) 18 as a control device.

The ECU 18 is configured as a computer including a microprocessor and peripheral circuits such as ROM and RAM necessary for its operation. The ECU 18 refers to input signals 19 from various sensors, performs various arithmetic processes necessary for operation control of the engine 1, transmits an output signal 20 to various devices, and executes operation control thereof. For example, the ECU 18 refers to an input signal from the air flow meter 21 to control the fuel injection amount of the fuel injection valve 12 so that an air-fuel mixture having a predetermined air-fuel ratio is formed, and outputs output signals from the crank angle sensor and the water temperature sensor. Referring to, the opening degree (duty ratio) of the EGR valve 14 is controlled. As a sensor referred to by the ECU 18, there is an oil temperature sensor that outputs a signal corresponding to the lubricating oil temperature of the engine 1 in addition to the above sensor. The water temperature sensor outputs a signal corresponding to the coolant temperature of the engine 1, and the crank angle sensor outputs a signal corresponding to the crankshaft angle.
The ECU 18 functions as a device that controls the opening degree of the EGR valve 14 by executing a predetermined program.

FIG. 2 is a flowchart showing an EGR rate correction amount calculation routine executed by the ECU 18 at an appropriate period in order to calculate the EGR rate correction amount. In this routine, when the engine is started in the homogeneous combustion operation in step S1, the ECU 18 sets the initial combustion chamber temperature T _C0 in step S2. A cooling water temperature or an oil temperature is adopted as the initial combustion chamber temperature T _C0 . This is because the initial combustion chamber temperature is the same as the coolant temperature or the lubricating oil temperature when the engine is not started. In step S3, an integrated injection amount Q obtained by integrating the fuel injection amount from the start to the present is calculated.

In the following step S4, the combustion chamber temperature T _C is calculated by the following calculation formula. In the present embodiment, the combustion chamber temperature T _C employs the piston surface temperature as a representative value, and the piston surface temperature is calculated by the following calculation formula. Since the piston surface temperature that most affects combustion is the representative value of the combustion chamber temperature, the correction accuracy of the EGR rate is the best. During stratified combustion operation, fuel injection is performed near the compression top dead center, and fuel spray collides with the piston surface and burns, so the piston surface temperature has the most influence on combustion.
T _C = T _C0 + F (Q)

However, F (Q) is an increase amount of the piston surface temperature from the initial temperature T _C0 and is a function related to the integrated injection amount Q. The function is obtained by simulation calculation or the measurement result of the piston surface temperature. The amount of increase in the piston surface temperature from the initial temperature is directly related to the integrated value of the amount of fuel injected and burned up to that point, and is determined by heat transfer and heat balance due to the combustion energy of the integrated value fuel. It is.

Note that the combustion chamber temperature T _C may be a temperature at an arbitrary location in the combustion chamber other than the piston surface temperature. In this case, F (Q) is the amount of increase from the initial temperature T _{C0 at the} arbitrary location.

In step S5, it is compared whether or not the cooling water temperature T _X is equal to or higher than a reference temperature T _X1 (for example, 80 ° C.) for switching to stratified combustion. Coolant temperature T _X is equal to or the reference temperature or more, the process proceeds to step S6. Otherwise, the process returns to step S3, and the integrated injection amount Q is recalculated. Steps S1 to S5 are the first warm-up operation.
In step S6, the engine operation is switched to the stratified combustion operation. That is, the execution is switched from the execution in the intake stroke of the fuel injection to the execution in the compression stroke. In step S7, a difference ΔT _C between a target combustion chamber temperature T _C1 (for example, 150 ° C.) serving as a reference for ending the second warm-up operation and the estimated combustion chamber temperature T _C is calculated, and the process proceeds to step S8. In step S8, it is determined whether or not ΔT _C is positive. If it is positive, the process proceeds to step S9, and if it is zero or negative, the process proceeds to step S10.

In step S9, an EGR rate correction amount ΔEGR is calculated based on ΔT _C , engine speed, and load. The four parameters form a map, and ΔEGR is read from this map. If [Delta] T _C is small, DerutaEGR also reduced.
If ΔT _C is zero or negative, it indicates that the second warm-up operation is finished and the steady operation state is reached, so that the process proceeds to step S10 and ΔEGR is set to zero. That is, no correction is made.

From step S9 or step S10, the process proceeds to step S11, the required EGR rate EGR ₁ immediately after switching to the stratified combustion operation is calculated by the following formula, and the process proceeds to step S12.
EGR ₁ = EGR ₀ −ΔEGR
Where EGR ₀ = EGR rate during steady operation
EGR ₁ = EGR rate during the second warm-up operation Note that the steady operation is a stratified combustion operation after the second warm-up operation is completed, that is, the piston surface temperature is equal to or higher than the target combustion chamber temperature (for example, 150 ° C.). The stratified combustion operation in the state where it is. The second warm-up operation refers to a stratified combustion operation until the piston surface temperature reaches a target combustion chamber temperature (for example, 150 ° C.) after completion of the first warm-up operation. The first warm-up operation refers to a homogeneous combustion operation from when the engine is started until the water temperature reaches a reference temperature (for example, 80 ° C.).

In step S12, the control based on the opening degree of the EGR control valve in EGR _1. Thereafter, the process proceeds to step S13 and returns to step S3. Steps S6 to S13 are the second warm-up operation. This completes the process of FIG.

  With the above control flow, intermittent combustion at the time of transition can be suppressed by performing EGR less than the EGR rate during steady operation at the time of transition to stratified combustion operation immediately after startup. Further, at the time of the transition, the combustion chamber temperature does not rise to the temperature at the time of steady operation and the generation of NOx is small, so that the harmful effects of NOx generation due to performing EGR less than the EGR rate at the time of steady operation are also small.

1 is an engine control device according to an embodiment of the present invention. The flowchart of the control apparatus which concerns on embodiment of this invention is shown.

Explanation of symbols

T _C Combustion chamber temperature T _C0 Initial combustion chamber temperature T _C1 Target combustion chamber temperature T _X Water temperature T _X1 Reference water temperature for switching to stratified combustion EGR ₀ EGR rate during steady operation EGR ₁ EGR rate during warm-up operation ΔEGR EGR rate Correction amount 1 Engine 2 Piston 3 Cylinder 4 Combustion chamber 5 Intake valve 6 Exhaust valve 7 Intake passage 8 Exhaust passage 9 Catalyst 10 Spark plug 11 Throttle valve 12 Fuel injection valve 13 EGR passage 14 EGR valve 15 Lean NOx catalyst 18 Engine control unit ( ECU)
19 Input signal 20 Output signal

Claims (4)

A control device for a direct injection engine that switches between homogeneous combustion operation and stratified combustion operation according to the operating conditions of the engine, and executes EGR during stratified combustion operation,
At start-up, the homogeneous combustion operation as the first warm-up operation is performed until the cooling water temperature reaches the reference temperature, and from the time when the cooling water temperature reaches the reference temperature until the combustion chamber temperature reaches the target combustion chamber temperature. Stratified combustion operation as the second warm-up operation, and when the combustion chamber temperature reaches the target combustion chamber temperature, the stratified combustion operation as the steady operation is continuously executed,
During the second warm-up operation, the EGR rate is corrected to be lower than the EGR rate during steady operation according to the combustion chamber temperature.   The control device according to claim 1, wherein the combustion chamber temperature employs a piston surface temperature as a representative value.   The control device according to claim 1, wherein the combustion chamber temperature is estimated as a sum of an initial combustion chamber temperature and a function of an integrated injection amount.   The control device according to claim 3, wherein the initial combustion chamber temperature employs the cooling water temperature or the lubricating oil temperature as a representative value.

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