JP2002004903A - Engine with supercharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine with a supercharger, capable of surely avoiding knocking in a uniform combustion region and surely suppressing the increase of NOx and the occurrence of smoke and over-torque by controlling a supercharging pressure in accordance with parameters correlated to engine torque in a stratified combustion region. SOLUTION: During stratified combustion operation, the supercharger is controlled in accordance with a target mean effective pressure to achieve good control responsiveness (Step 816, 18). During uniform combustion operation, the supercharger is controlled in accordance with the supercharging pressure to establish supercharging pressure control without being affected by a difference in set air/fuel ratio (Step S6, 8).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supercharged engine that switches between a uniform combustion operation and a stratified combustion operation according to an operation state.

[0002]

2. Related Background Art In recent years, in-cylinder injection engines for directly injecting fuel into a combustion chamber for the purpose of improving fuel efficiency and reducing emissions have been put into practical use. In this type of engine, in addition to the usual uniform combustion operation, In this stratified combustion operation, a lean air-fuel ratio is present around the ignitable mixture near the stoichiometric mixture while the lean air-fuel ratio is present around the spark plug, thereby achieving a lean overall air-fuel ratio. Has been realized.

On the other hand, this type of direct injection type engine may be provided with a supercharger. In this case, the supercharging pressure is controlled in order to avoid knock caused by excessive supercharging pressure. It is conceivable to regulate the upper limit of the supercharging pressure with a wastegate valve or the like. Since knock occurs at a high load with a high in-cylinder temperature, the regulation of the upper limit supercharging pressure is mainly performed during the uniform combustion operation. However,
If the air becomes excessive in the stratified charge combustion operation, NOx (nitrogen oxide) is generated. Therefore, supercharging pressure control for preventing NOx is required in the stratified charge combustion region. Control is also required to suppress the supercharging pressure in the sense that the engine torque is limited to the allowable in-cylinder pressure or the allowable input torque of the transmission. However, since this excessive torque occurs also in the stratified combustion region, For that reason, supercharging pressure control is required in the stratified combustion region.

Although the intake air amount can be limited by suppressing the throttle opening instead of the supercharging pressure control, the supercharger at this time is driven by the engine to continue the same compression work as at full load. In a supercharger, the drive loss increases, and suppressing the throttle opening halves the merit of the stratified combustion region in which the pumping loss can be reduced. Therefore, it is desirable to limit the intake air amount by adjusting the supercharging pressure, and it is conceivable to perform the same supercharging pressure control in the stratified combustion region as in the uniform combustion region.

[0005]

However, in the stratified charge combustion region, the air-fuel ratio is controlled on the lean side based on the operating state of the engine. Therefore, even at the same supercharging pressure, the fuel injection is performed in accordance with the set air-fuel ratio. As the amount increases or decreases, the engine torque differs. That is, since the supercharging pressure does not reflect the engine torque, the control based on the supercharging pressure cannot be realized in the stratified combustion region and cannot be realized.

On the other hand, for example, Japanese Patent Application Laid-Open No. 23226/1990 discloses a technique for preventing a fuel shortage by lowering a supercharging pressure when a required fuel amount of an engine exceeds a maximum injection amount of a fuel injection valve. However, it is conceivable to control the supercharging pressure in both the uniform combustion and the stratified combustion based on the fuel amount. However, when the supercharging pressure control is performed based on the fuel amount, there is a problem that a control delay occurs in a uniform combustion region. That is, since the supercharging pressure is considered together with the intake air amount and the engine rotation speed in setting the fuel injection amount, the change in the supercharging pressure is indirectly reflected in the supercharging pressure control via the fuel injection amount. As a result, a control delay of at least one stroke occurs. Therefore, for example, during a transition such as acceleration, control based on a change in the fuel injection amount delays suppression of the supercharging pressure, and knocking may not be avoided.

SUMMARY OF THE INVENTION It is an object of the present invention to reliably avoid knocking in a uniform combustion region and to control supercharging pressure based on a parameter correlated with engine torque in a stratified combustion region to reliably suppress NOx and excessive torque. It is an object of the present invention to provide a supercharged engine capable of performing the following.

[0008]

In order to achieve the above object, the invention of claim 1 provides a supercharger and a supercharger for an engine that switches between a uniform combustion operation and a stratified combustion operation according to an operation state. Control means for controlling the supercharger based on the target torque correlation value during the stratified combustion operation, and based on the supercharging pressure during the uniform combustion operation. Is controlled.

Therefore, during the uniform combustion operation, the supercharger is controlled based on the supercharging pressure, so that good control responsiveness is realized, and during the stratified combustion operation, the target torque correlation value correlated with the engine torque. , The supercharger can be controlled without being affected by the difference in the set air-fuel ratio. According to a second aspect of the present invention, the supercharger control means includes a bypass passage provided in the intake passage, which connects the upstream intake passage and the downstream intake passage of the supercharger, and a bypass valve provided in the bypass passage. And bypass valve control means for controlling the degree of opening of the bypass valve.

Accordingly, when the opening of the bypass valve is controlled by the bypass valve control means, the amount of intake air recirculated from the downstream side to the upstream side of the turbocharger via the bypass passage changes,
The boost pressure is adjusted accordingly. Further, according to a third aspect of the present invention, the turbocharger is a turbocharger, and the supercharger control means is a wastegate passage connecting an upstream exhaust passage and a downstream exhaust passage of a turbine of the turbocharger provided in the exhaust passage. And a wastegate valve provided in the wastegate passage, and wastegate valve control means for controlling the opening of the wastegate valve.

Therefore, when the opening of the wastegate valve is controlled by the wastegate valve control means, the amount of exhaust gas relieved by bypassing the turbine through the wastegate passage is adjusted, and the supercharging pressure is adjusted accordingly. Is done.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment in which the present invention is embodied in a direct injection type engine with a roots type supercharger will be described below. FIG. 1 is an overall configuration diagram showing a direct injection engine with a supercharger according to a first embodiment. As shown in the figure, an engine 1 is configured as a direct injection gasoline engine, and a cylinder head of the engine 1 is provided with a spark plug 2 for each cylinder.
At the same time, an electromagnetic fuel injection valve 3 is attached, and fuel is directly injected into the combustion chamber 4 from the fuel injection valve 3. An intake port 5 of each cylinder formed in the cylinder head is connected to a common intake passage 6, and a supercharger driven by the engine 1 from an upstream side through an air cleaner 7 and a belt (not shown) through the intake passage 6. Roots type supercharger 8, an intercooler 9 for cooling intake air, and a throttle valve 11 driven to be opened and closed by a step motor 10 in response to an accelerator operation.

The intake air introduced into the intake passage 6 through the air cleaner 7 is compressed by the supercharger 8 and cooled by the intercooler 9, and then passes through the throttle valve 11 and opens the intake valve 12. And is introduced into the combustion chamber 4. An exhaust port 14 of each cylinder formed in the cylinder head is connected to a common exhaust passage 15, and a catalyst and a muffler (not shown) are provided in the exhaust passage 15. The intake air introduced into the combustion chamber 4 mixes the fuel injected from the fuel injection valve 3 and burns by ignition of the spark plug 2, and the exhaust gas after the combustion is exhausted along with the opening of the exhaust valve 16. Is discharged to the outside.

A supercharger 8 is provided in the intake passage 6.
Is provided, and a bypass valve 18 is provided in the bypass passage 17. The bypass valve 18 is driven to open and close by a step motor 19. On the other hand, an ECU (electronic control unit) 21 including an input / output device, a storage device (ROM, RAM, and the like), a central processing unit (CPU), a timer counter, and the like is installed in the vehicle interior. On the input side of the ECU 21,
A Karman vortex air flow meter 22 for detecting an intake air amount Q introduced into the intake passage 6, a rotation speed sensor 23 for detecting a rotation speed Ne of the engine 1, and an accelerator sensor 24 for detecting a driver's accelerator operation amount APS. Are connected, and detection information from these sensors is input. On the output side of the ECU 21, the above-described ignition plug 2,
The fuel injection valve 3, the step motors 10, 19 and the like are connected. In the present embodiment, a supercharger control unit is configured by the bypass passage 17, the bypass valve 18, and the ECU 21.

The ECU 21 performs comprehensive control of the engine 1 based on information input from each sensor. For the fuel injection amount control, the accelerator operation amount AP
A target average effective pressure Pe (representing an engine load) is obtained from the engine speed S and the engine rotation speed Ne, and the optimum operating area is determined from the target average effective pressure Pe and the engine rotation speed Ne according to a preset map shown in FIG. And a target air-fuel ratio.

For example, in a low-load low-speed range such as during idling or low-speed running, a stratified combustion region in the figure is set, and the target air-fuel ratio is set to a lean side to execute fuel injection in the compression stroke. Is done. As is well known, in this compression stroke injection, the injected fuel is guided to the vicinity of the ignition plug 2, and the ignitable mixture near the stoichiometric fuel mixture is concentrated around the ignition plug 2, and a mixture having a lean air-fuel ratio is formed therearound. With the presence of air, combustion is performed at a lean overall air-fuel ratio to improve fuel efficiency. Further, in a high-load and high-speed region such as during acceleration, a uniform combustion region in the drawing is set, and the target air-fuel ratio is set to the stoichiometric or rich side, and fuel injection is executed in the intake stroke. In this intake stroke injection, the injected fuel generates a uniform air-fuel mixture to ensure engine torque.

On the other hand, the supercharging pressure of the supercharger 8 is controlled by the ECU 21 by adjusting the opening of the bypass valve 18. As shown in FIGS. 1 and 3, when the bypass valve 18 is fully closed, all the intake air discharged from the supercharger 8 is supplied to the engine 1 to obtain a maximum pressure ratio, while the supercharger 8 is closed. The driving loss is maximized. When the opening degree of the bypass valve 18 increases, the amount of intake air recirculated from the downstream side to the upstream side of the supercharger 8 via the bypass passage 17 increases and the pressure ratio decreases, while the drive loss of the supercharger 8 decreases I do. Assuming such characteristics, in order to avoid knocking and to prevent misfire in the uniform combustion region, as described later,
In the stratified combustion region, the ECU 21 controls the opening of the bypass valve 18 for the purpose of suppressing NOx and suppressing excessive torque.

Next, the supercharging pressure control executed by the ECU 21 of the in-cylinder injection type engine with a supercharger configured as described above will be described. FIG. 4 shows a bypass valve control routine executed by the ECU 21. The ECU 21 executes this routine at predetermined control intervals. This routine controls the bypass valve 18 in the fully closed state to the open side. First, in step S2, detection information from each sensor is input, and in step S4, the target average effective pressure P
Based on e and the engine speed Ne, it is determined from the map whether or not the current operation region is a stratified combustion region. If it is in the uniform combustion region, a negative (NO) determination is made, and the routine proceeds to step S6, where the target supercharging pressure Ptgt is calculated. This calculation process is general, and calculates the target boost pressure Ptgt from a preset map based on the accelerator operation amount APS and the engine rotation speed Ne.

Then, at step S8, the target boost pressure Ptg
The opening degree θb of the bypass valve 18 required to achieve t is calculated. In step S10, the step motor 10 is driven to keep the throttle valve 11 fully open, and the step motor 19 is driven to open the bypass valve 18. Degree, and then terminate the routine. As a result, the intake air amount corresponding to the opening degree of the bypass valve 18 is returned from the downstream side to the upstream side of the supercharger 8 via the bypass passage 17, and the supercharging pressure is adjusted accordingly. For example, in a region where the load is not particularly high in the uniform combustion region, the bypass valve 18 is controlled to an opening degree near the fully closed state to secure the supercharging pressure. The supply pressure is suppressed to avoid knocking due to an increase in the cylinder temperature or to prevent misfire due to excessive intake air.

On the other hand, if it is determined in step S4 that the engine is in the stratified combustion region, a YES (affirmative) determination is made and step S12 is performed.
Then, the target average effective pressure Pe is calculated. This calculation process is the same as that performed in the combustion injection control on the engine 1 side, and the target average effective pressure Pe is obtained from the accelerator operation amount APS and the engine rotation speed Ne. In the following step S14, it is determined whether or not the operating range requires the opening degree control of the bypass valve 18. Specifically, in the stratified combustion region, for example, when the intake air becomes excessive due to an increase in the supercharging pressure and NOx is generated, or when the supercharging pressure increases, the engine torque is reduced to the allowable in-cylinder pressure of the engine 1. When the input torque exceeds the allowable input torque of the transmission or the like, it is necessary to suppress the supercharging pressure.

In step S14, it is determined whether or not the engine 1 is operating in a region where these situations occur. If the determination is NO, the process returns to step S2.
Therefore, in this case, the boost pressure is not suppressed while the bypass valve 18 is kept in the fully closed state. If the determination in step S14 is YES, the intake air amount Q is detected in step S16, and the opening degree of the bypass valve 18 required to achieve the target average effective pressure Pe is determined in step S18.
It is calculated according to the following procedure.

FIG. 5 shows a map for setting the target intake air amount Qa, and FIG. 6 shows a map for setting the bypass valve opening θb. In the map of FIG.
x and an intake air amount capable of suppressing excessive torque (specifically, an intake air amount capable of achieving an air-fuel ratio capable of suppressing NOx and not generating excessive torque exceeding the allowable input torque of the transmission). ) Is set as the target intake air amount Qa. First, the ECU 21 sets a target intake air amount Qa from the target average effective pressure Pe and the engine rotation speed Ne based on this map. The map in FIG. 5 may be set for each intake air temperature.

Next, the difference ΔQ between the intake air amount Q detected by the air flow meter 22 and the target intake air amount Qa is calculated, and the bypass valve opening θb is set from the difference ΔQ based on the map shown in FIG. Then, the obtained bypass valve opening degree θb
In step S10, the step motor 19 is driven to adjust the opening of the bypass valve 18. Therefore, the opening degree of the bypass valve is controlled so that the actual intake air amount Q converges to the target intake air amount Qa. As a result, the engine 1 is maintained in an operating state in which NOx and excessive torque are suppressed. You.

As described above, in the in-cylinder injection type engine 1 with a supercharger according to the first embodiment, during the uniform combustion operation, the bypass valve 18 is controlled based on the supercharging pressure. The supercharging pressure is suppressed without causing the occurrence of knocking due to a rise in the cylinder temperature and an increase in the generation of NOx due to excessive intake air and a misfire. In addition, during the stratified charge combustion operation, the supercharging pressure is controlled based on the target average effective pressure Pe correlated with the engine torque. Therefore, the supercharging pressure control is established without being affected by the difference in the set air-fuel ratio, and NOx And excessive torque can be reliably suppressed.

Further, when the supercharging pressure is limited by the control on the closing side of the bypass valve 18, the driving loss of the supercharger 8 is reduced and the pumping loss due to the suppression of the throttle opening APS does not occur. , Fuel efficiency can be improved. In the first embodiment, a part of the intake air is recirculated in the bypass passage 17 to adjust the supercharging pressure of the supercharger 8. For example, the input pulley of the supercharger 8 is provided with an electromagnetic clutch, The supercharging pressure may be controlled by limiting the operating state of the supercharger 8 by controlling the connection and disconnection of the clutch. Alternatively, a transmission may be provided between the crankshaft of the engine 1 and the supercharger 8 to change the speed thereof. The supercharging pressure may be controlled by changing the rotation speed of the supercharger 8 according to the state. [Second Embodiment] Hereinafter, a second embodiment in which the present invention is embodied in a direct injection type engine with a turbocharger will be described.

FIG. 7 is an overall structural view showing a direct injection type engine with a turbocharger according to a second embodiment. As shown in the figure, the configuration of the engine 1 itself is the same as that of the first embodiment, and a compressor 31a of a turbocharger 31 as a supercharger is provided in the intake passage 6 of the engine 1 instead of the supercharger 8. ing. Exhaust passage 1
5 is provided with a turbine 31b of the turbocharger 31 coaxially connected to the compressor 31a, and the exhaust gas flowing through the exhaust passage 15 drives the turbine 31b to rotate, so that the compressor 31a exerts a compression action of the intake air. .

The turbine 31b has an exhaust passage 1 on the upstream side.
A wastegate passage 32 that connects the exhaust passage 5 and the exhaust passage 15 on the downstream side is provided, and an actuator 35 is connected to a wastegate valve 33 disposed in the wastegate passage 32 via a rod 34. Actuator 35
Is connected to the downstream side of the compressor 31a via the first pipe 36, and is connected to the compressor 3 via the second pipe 37.
The second pipe 37 is connected to the upstream side of the valve 1a, and is opened and closed by a solenoid valve 38.

The compressor 31 acting on the first conduit 36
The supercharging pressure on the downstream side is relieved toward the second pipe line 37 substantially equal to the atmospheric pressure in accordance with the open / close state of the solenoid valve 38, and as a result, the pressure acting on the actuator 35 is adjusted. The rod 34 is operated to a position where this pressure and the compression spring 35a in the actuator 35 are balanced,
The opening of the wastegate valve 33 is adjusted accordingly, and the amount of exhaust gas relieved by bypassing the turbine 31b via the wastegate passage 32 is adjusted.

On the other hand, the solenoid valve 38 is connected to the output side of the ECU 21 in place of the bypass valve 18 of the first embodiment, and the duty of the solenoid valve 38 is controlled.
In the present embodiment, a supercharger control unit is configured by the wastegate passage 32, the wastegate valve 33, and the ECU 21. Then, the ECU 21 controls the fuel injection amount of the engine 1 and the like as in the first embodiment,
The supercharging pressure of the turbocharger 31 is controlled.

FIG. 8 shows a solenoid valve control routine executed by the ECU 21. The ECU 21 executes this routine at a predetermined control interval. First, similarly to the first embodiment, detection information from each sensor is input in step S22, and it is determined in step S24 whether the current operation region is a stratified combustion region. If it is in the uniform combustion region, the determination is NO and the process proceeds to step S26, where the accelerator operation amount APS is set.
Then, the target boost pressure Ptgt is calculated from the engine speed Ne and the opening degree θw of the wastegate valve 33 required to achieve the target boost pressure Ptgt is calculated in step S28.
In the following step S30, the duty of the solenoid valve 38 is controlled to adjust the opening of the waste gate valve 33, and then the routine is terminated. By the control described above, in the uniform combustion region, it is possible to avoid knocking due to an increase in the in-cylinder temperature or to prevent misfire due to excessive intake air.

On the other hand, if it is determined in step S24 that the engine is in the stratified charge combustion region, a determination of YES is made, and the routine proceeds to step S32, where the accelerator operation amount APS is determined based on a map (not shown).
And the target average effective pressure Pe from the engine rotation speed Ne. The target average effective pressure Pe at this time is set to a value that can suppress NOx, smoke, and excessive torque exceeding the allowable input torque of the transmission. In step S34, the opening degree θw of the wastegate valve 33 necessary to achieve the target average effective pressure Pe is set, and based on the opening degree θw, the duty of the solenoid valve 38 is controlled in step S30, and the wastegate valve 33 is adjusted for opening.

As described above, in the in-cylinder injection type engine 1 with a turbocharger according to the second embodiment, during the uniform combustion operation, the wastegate valve 33 is controlled based on the supercharging pressure. Thus, the supercharging pressure is suppressed without causing the occurrence of knocking and misfire due to excessive intake air due to the rise in the cylinder temperature. In addition, during the stratified charge combustion operation, the supercharging pressure is controlled based on the target average effective pressure Pe correlated with the engine torque. Therefore, the supercharging pressure control is established without being affected by the difference in the set air-fuel ratio, and NOx And excessive torque can be reliably suppressed.

Although the embodiment has been described above, aspects of the present invention are not limited to this embodiment. For example, in the first and second embodiments, the supercharging pressure is controlled based on the target average effective pressure Pe in the stratified combustion region, but the supercharging pressure control can be established if the parameter is correlated with the engine torque. For this reason, the supercharging pressure control may be performed based on, for example, the fuel amount and the volumetric efficiency.

In the first and second embodiments, the supercharging pressure is suppressed in order to avoid knocking in the uniform combustion region. However, for example, in a high speed and high load region, the required fuel amount of the engine 1 is reduced by the fuel injection valve. Even when the appropriate air-fuel ratio cannot be maintained beyond the maximum injection amount of 3, the supercharging pressure may be suppressed by the same processing as in the first and second embodiments, so that an appropriate air-fuel ratio may be maintained.

Further, in the first embodiment, the supercharger 8 is used as the supercharger, and in the second embodiment, the turbocharger 31 is used as the supercharger. However, the type is not limited to this. For example, a Richolm-type or spiral-type supercharger may be applied.

[0036]

As described above, according to the supercharged engine of the present invention, knock can be reliably avoided in the uniform combustion region, and the supercharging pressure is determined based on the parameter correlated with the engine torque in the stratified combustion region. By controlling NOx, smoke and excessive torque.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram illustrating a direct injection engine with a supercharger according to a first embodiment.

FIG. 2 is an explanatory diagram showing a map in which an operation area is set.

FIG. 3 is an explanatory diagram showing a relationship between a bypass valve opening, a pressure ratio, and a drive loss.

FIG. 4 is a flowchart illustrating a bypass valve control routine executed by the ECU.

FIG. 5 is an explanatory diagram showing a map for setting a target intake air amount.

FIG. 6 is an explanatory diagram showing a map for setting a bypass valve opening.

FIG. 7 is an overall configuration diagram illustrating a direct injection engine with a turbocharger according to a second embodiment.

FIG. 8 is a flowchart showing a solenoid valve control routine executed by the ECU.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 In-cylinder injection engine 6 Intake passage 8 Supercharger (supercharger) 15 Exhaust passage 17 Bypass passage (supercharger control means) 18 Bypass valve (supercharger control means) 21 ECU (supercharger control means, bypass) Valve control means, wastegate valve control means) 31 turbocharger (supercharger) 31b turbine 32 wastegate passage (supercharger control means) 33 wastegate valve (supercharger control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301K 301R // F02B 33/00 F02B 33/00 E 37/18 37 / 12 302Z 37/12 302 301A F term (reference) 3G005 EA05 EA19 FA02 FA22 GB18 GB28 GC07 JA06 JA22 JA24 JA39 JA45 3G084 BA05 BA07 BA09 BA13 DA02 DA10 DA35 FA07 FA10 FA12 FA26 FA33 3G092 AA01 AA06 AA09 AA18 BA02 BA04 BA05 BA05 DB03 DC01 DC04 DC12 DE03S DG06 DG08 DG09 EA13 FA16 FA17 FA24 FA39 GA03 HA01X HA01Z HA06X HA16X HC01Z HD09X HE01Z HF08Z 3G301 HA01 HA04 HA11 JA02 JA22 JA25 KA06 LA03 LB04 MA01 MA11 PA01Z PA11Z PA01Z PC01Z

Claims (3)

[Claims] 1. An engine for switching between a uniform combustion operation and a stratified combustion operation in accordance with an operation state, comprising: a supercharger; and supercharger control means for controlling the supercharger. Means for controlling the supercharger based on the target torque correlation value during the stratified combustion operation, and controlling the supercharger based on the supercharging pressure during the uniform combustion operation. 2. The supercharger control means includes: a bypass passage provided in an intake passage, which connects an upstream intake passage and a downstream intake passage of the supercharger; a bypass valve provided in the bypass passage; The engine with a supercharger according to claim 1, further comprising: bypass valve control means for controlling an opening degree of the bypass valve. 3. The turbocharger is a turbocharger, and the supercharger control means includes a wastegate passage provided in an exhaust passage and connecting an upstream exhaust passage and a downstream exhaust passage of a turbine of the turbocharger. The engine with a supercharger according to claim 1, further comprising: a wastegate valve provided in the wastegate passage; and a wastegate valve control means for controlling an opening degree of the wastegate valve.