Patent Application
20090025682
This application is based on Japanese Patent Application No. 2007-191509 filed on Jul. 24, 2007, the disclosure of which is incorporated herein by reference.
The present invention relates to a controller for a spray-guide type direct injection engine in which fuel is injected into a combustion chamber from a substantial upper center of the combustion chamber.
Generally, a direct injection engine has a fuel injector which obliquely downwardly injects fuel into a combustion chamber from a side wall of the combustion chamber (vicinity of the intake port). The injected fuel collides with a recess formed on a top surface of a piston, and is guided to an upper part of the piston by an inner peripheral wall of the recess. Such an injection method is called a wall-guide type injection.
If the injected fuel adheres to the piston top surface or the cylinder inner wall surface, the adhering fuel will remain as uncombusted hydrocarbon (HC). When the fuel (wet) adhering to the piston top surface or the cylinder inner wall surface increases, a quantity of discharged HC increases to deteriorate exhaust emission.
In order to solve the above problems, a spray-guide type (center injection type) direct injection engine has been developed. The spray-guide type direct injection engine, as shown in JP-2005-105877A, has a fuel injector which downwardly injects the fuel into a combustion chamber from a substantial upper center of a combustion chamber. An injection force (penetrating force) of the fuel is established in such a manner that the injected fuel does not collide with a piston upper surface and a cylinder inner surface, so that amount of fuel adhering on the piston upper surface and the cylinder inner surface can be decreased.
In the spray-guide type direct injection engine, as shown in
Since the spark plug 20 is fixed by fastening a thread part 39 formed in an outer peripheral of a metal housing into a screw-thread plug hole 40 of the cylinder head 31, the direction of the ground electrode 38 changes due to manufacture dispersion of thread-part 39 and the screw-thread plug hole 40, and dispersion of the fastening force of the spark plug 20. As mentioned above, in the spray-guide type direct injection engine, the ground electrode 38 protruding to the fuel-spray area SA serves as the obstacle which interrupts a part of fuel-spray. Therefore, if the direction of the ground electrode 38 changes, a shape of the fuel-spray is also changed.
Generally, in the direct injection engine, according to the engine operation conditions (engine speed, required torque, etc.), an injection mode (combustion mode) is switched between a homogeneous combustion mode (intake stroke injection mode), a stratified combustion mode (compression stroke injection mode), and a weak stratified combustion mode (intake-compression stroke divided injection mode). In the homogeneous combustion mode where the fuel is injected in the intake stroke, since the combustion chamber is filled with the homogeneous air-fuel mixture, the combustion state does not change due to the direction of the ground electrode 38. In the stratified combustion mode and the weak stratified combustion mode in which the fuel is injected in the compression stroke, the thick air-fuel mixture is partially formed at a vicinity of the spark-plug 20. Hence, if a state of the fuel-spray changes due to the direction of the ground electrode 38, the state of the air-fuel mixture at a vicinity of the spark-plug 20 is changed and the combustion state is changed. For this reason, as shown in
The present invention is made in view of the above matters, and it is an object of the present invention to provide a controller for a spray-guide type direct injection engine, which is able to prevent deterioration of a combustion state due to a direction of the ground electrode of the spark plug, and to realize favorable stratified combustion and weak stratified combustion which are not influenced by the direction of the ground electrode of the spark plug.
According to the present invention, a controller includes a fuel injector which directly injects fuel into a combustion chamber from a substantial upper center of the combustion chamber, and a fuel injection control means for performing a fuel injection in a compression stroke injection mode in which the fuel is injected in a compression stroke to perform a stratified combustion or in an intake-compression stroke divided injection mode to perform a weak stratified combustion. The controller further includes a combustion state determination means for determining a combustion state in each cylinder while the fuel injection is performed in the compression stroke injection mode or the intake-compression stroke divided injection mode. When the combustion determination means detects a combustion deterioration in any cylinders, the fuel injection control means performs a combustion improvement control in which the fuel injection which is supposed to be performed in one compression stroke is divided into a plurality of fuel injections in the compression stroke with respect to the cylinder or all cylinders.
Thereby, the fuel quantity per one fuel injection is decreased and the penetrating force of the fuel-spray is reduced. The adverse effect of the ground electrode to the fuel-spray becomes small, and the forming condition of the air-fuel mixture around the spark plug is improved. The deterioration of the combustion condition due to the direction of the ground electrode of the spark plug can be avoided. The stratified combustion and the weak stratified combustion can be well performed without respect to the direction of the ground electrode of the spark plug.
According to another aspect of the invention, in a case that the fuel injection is divided into two injections in one compression stroke when the combustion deterioration is detected, the fuel-injection-terminate timing of the second injection may be set to the fuel-injection-terminate timing of a case that the fuel injection is not divided, and the fuel-injection-terminate timing of the first injection can be close to the fuel-injection-start timing of the second injection.
Alternatively, in a case that the fuel injection is divided into two injections in one compression stroke, the fuel injection quantity in the first injection can be set smaller than that in the second injection.
According to another aspect of the invention, the controller further includes an ignition control means. When a combustion deterioration is detected in any cylinders by the combustion state determination means, the ignition control means performs a combustion improvement control in which a total spark period in the cylinder or all cylinders is prolonged in a retard direction.
A multi-point ignition can be performed in order to prolong the total spark period in the retard direction.
In performing the multi-ignition when the combustion deterioration is detected, the spark period per one spark may be made shorter than usual and the number of spark may be set greater than usual.
Alternatively, in performing the multi-ignition when the combustion deterioration is detected, the spark period per one spark may be made longer than usual and the number of spark is set less than usual.
Alternatively, the combustion improvement control can be performed by correcting the fuel injection timing to be advanced in a compression stroke.
Alternatively, the combustion improvement control can be performed by correcting the ignition timing to be retarded in a compression stroke.
The controller may include an intake air quantity control means which increases the intake air flow rate to restrict a torque decrease when the torque is decreased due to an execution of the combustion improvement control.
The controller may include the fuel pressure control means which performs a combustion improvement control in which the fuel pressure is reduced, when the combustion deterioration of any cylinders is detected.
Other objects, features and advantages of the present invention will become more apparent from the following description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:
An embodiment of the present invention will be described hereinafter.
Referring to
A fuel injector 19 is provided on a cylinder head 31 of the engine 11 to inject fuel directly into each cylinder. The fuel discharged from a high-pressure fuel pump 21 is sent to a delivery pipe 23 through a fuel pipe 22, and is distributed to the fuel injector 19 of each cylinder from this delivery pipe 23. The fuel pressure sensor 24 which detects pressure (fuel pressure) of the fuel supplied to the fuel injector 19 is attached to the delivery pipe 23.
As shown in
As shown in
As shown in
A coolant temperature sensor 29 detecting a coolant temperature, and a crank angle sensor 30 outputting a pulse signal every predetermined crank angle of a crankshaft of the engine 11 are disposed on a cylinder block of the engine 11. A crank angle and an engine speed are detected based on the output signal of the crank angle sensor 30.
The outputs of the sensors are inputted to an electronic control unit (ECU) 37. The ECU 37 includes a microcomputer which executes an engine control program stored in a Read Only Memory (ROM) to control a fuel injection quantity and an ignition timing according to an engine operation condition.
According to the engine operation conditions (engine speed, required torque, etc.), the ECU 37 switches an injection mode (combustion mode) between a compression stroke injection mode (stratified combustion mode), an intake-compression stroke divided injection mode (weak stratified combustion mode), and an intake stroke injection mode (homogeneous combustion mode). In the compression stroke injection mode (stratified combustion mode), a little amount of fuel is directly injected into the cylinder during a compression stroke. A stratified air-fuel mixture is formed at a vicinity of the spark plug 20 to perform a stratified combustion (lean combustion) to improve fuel economy. In the intake-compression stroke divided injection mode (weak stratified combustion mode), the fuel is injected in the intake stroke and the compression stroke. In the intake stroke, a thin homogeneous air-fuel mixture is formed, and in the compression stroke, a thick stratified air-fuel mixture is formed near the spark plug 20 to perform the weak stratified combustion. In the intake stroke injection mode (homogeneous combustion mode), a fuel injection quantity is increased and the fuel is directly injected into the cylinder during the intake stroke. A homogenous air-fuel mixture is formed to perform a homogeneous combustion to improve an engine output.
In the spray-guide type direct injection engine 11, as shown in
Since the spark plug 20 is fixed by fastening a thread part 39 formed in an outer peripheral of a metal housing into a screw-thread plug hole 40 of the cylinder head 31, the direction of the ground electrode 38 changes due to manufacture dispersion of thread-part 39 and the screw-thread plug hole 40, and dispersion of the fastening force of the spark plug 20. As mentioned above, in the spray-guide type direct injection engine, the ground electrode 38 protruding to the fuel-spray area SA serves as the obstacle which interrupts a part of fuel-spray. Therefore, if the direction of the ground electrode 38 changes, a shape of the fuel-spray is also changed.
In the suction stroke injection mode (homogeneous combustion mode), since the combustion chamber 32 is filled with the homogeneous air-fuel mixture, the combustion state does not change due to the direction of the ground electrode 38. In the stratified combustion mode and the weak stratified combustion mode in which the fuel is injected in the compression stroke, the thick air-fuel mixture is partially formed at a vicinity of the spark-plug 20. Hence, if the fuel-spray state changes due to the direction of the ground electrode 38, the state of the air-fuel mixture at a vicinity of the spark-plug 20 is changed and the combustion state is changed. For this reason, depending on the direction of the ground electrode 38, the combustion state may be deteriorated.
When the engine 11 is in the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode), the ECU 37 determines the combustion condition in each cylinder based on a variation in engine speed, a variation in incylinder pressure (combustion pressure), and a variation in combustion ion current. If a combustion deterioration is detected in any cylinders, the ECU 37 performs a combustion improvement control to improve the combustion condition.
In this embodiment, the combustion improve control is performed by at least one of five methods, which will be described hereinafter.
In a case of the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode), when a combustion deterioration is detected in any cylinders, one fuel injection which will be performed in one compression stroke is divided into multiple fuel injections in the compression stroke with respect to the deteriorated cylinder or all cylinders. Thereby, the fuel quantity per one fuel injection is decreased and the penetrating force of the fuel-spray is reduced. The adverse effect of the ground electrode 38 to the fuel-spray becomes small, and the forming condition of the air-fuel mixture around the spark plug 20 is improved.
According to the experiment conducted by the inventor, as the fuel-injection-terminate timing of a first injection in the divided injections becomes earlier, the emission is more deteriorated. Furthermore, when the fuel injection quantity of the first injection is greater than that of a second injection, the emission is deteriorated.
In a situation that the fuel injection is divided into two injections in one compression stroke and the combustion deterioration is detected, the fuel-injection-terminate timing of the second injection may be set to a fuel-injection-terminate timing of a case where the fuel injection is not divided, and the fuel-injection-terminate timing of the first injection can be close to the fuel-injection-start timing of the second injection as much as possible. Thereby, since the fuel-injection-terminate timing of the first injection is delayed, the deterioration of the emission can be avoided.
Alternatively, in a situation that the fuel injection is divided into two injections in one compression stroke, the fuel injection quantity in the first injection can be set smaller than that in the second injection. Since the fuel injection quantity in the first injection can be reduced, the deterioration of the emission can be avoided.
In a case of the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode) when a combustion deterioration is detected in any cylinders, a total spark period of the spark plug is prolonged in a retard direction with respect to the deteriorated cylinder or all cylinders. Hence, the ignition can be maintained until a retarded time when the combustion state is improved. The deterioration of the combustion condition due to the direction of the ground electrode of the spark plug can be avoided. The stratified combustion and the weak stratified combustion can be well performed without respect to the direction of the ground electrode of the spark plug.
A multi-point ignition can be performed in order to prolong the total spark period in the retard direction.
In a system where a multi-ignition is performed in the compression stroke injection mode or the intake-compression stroke injection mode, a spark period per one spark may be made shorter than usual and the number of spark may be set greater than usual. A dispersion of the total spark period in prolonging the total spark period by performing the multi-ignition can be reduced.
Alternatively, in performing the multi-ignition when the combustion deterioration is detected, the spark period per one spark may be made longer than usual and the number of spark is set less than usual. Thereby, the performance of ignition is improved when the multi-ignition is performed.
In a case of the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode), when a combustion deterioration is detected in any cylinders, a fuel injection timing in the cylinder is corrected to be advanced in the compression stroke. Since the fuel injection timing is advanced relative to the ignition timing, the ignition can be performed after the fuel injection is terminated. The ground electrode 38 hardly interrupts the fuel-spray so that the combustion state is improved. The stratified combustion and the weak stratified combustion can be performed well without respect to the direction of the ground electrode 38.
In a case of the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode), when a combustion deterioration is detected in any cylinders, an ignition timing in the cylinder is corrected to be retarded. Since the ignition timing is retarded relative to the fuel injection timing, the ignition can be performed after the fuel injection is terminated. The ground electrode 38 hardly interrupts the fuel-spray so that the combustion state is improved. The stratified combustion and the weak stratified combustion can be performed well without respect to the direction of the ground electrode 38.
In a case of the compression stroke injection mode (stratified combustion mode) or the intake-compression stroke divided injection mode (weak stratified combustion mode), when a combustion deterioration is detected in any cylinders, fuel pressure (discharge pressure of the fuel pump 21) supplied to the fuel injector 19 is decreased. Since the penetrating force of the fuel-spray is reduced by decreasing the fuel pressure at the detection of the combustion deterioration, the ground electrode 38 hardly interrupts the fuel-spray in the stratified combustion mode or the weak stratified combustion mode, so that the forming state of the air-fuel mixture at a vicinity of the spark plug 20 is improved. The stratified combustion and the weak stratified combustion can be performed well without respect to the direction of the ground electrode 38.
If two or more kinds of the combustion improvement control explained above are combined and performed, it may be able to enlarge the combustion improvement effect.
For example, the combustion improve control (1) and (2) may be combined. When the combustion deterioration is detected in any cylinders, one fuel injection which will be performed in one compression stroke is divided into multiple fuel injections in the compression stroke and a total spark period of the spark plug is prolonged in a retard direction with respect to the deteriorated cylinder or all cylinders. The total fuel injection period is prolonged and the total spark period is also prolonged. Thus, an ignition performance which is appropriate for the divided injection is ensured, and the combustion state is efficiently improved. The emission and the engine torque hardly receive adverse affect.
In a case of performing the combustion improve control (1)-(4), there is a possibility that the torque is decreased. When the torque is decreased, the opening degree of the throttle valve is increased to increase the intake air quantity. A torque decrease can be avoided during the combustion improve control so that the drivability is improved.
According to a combustion improve control routine shown in
Then, the procedure proceeds to step 102 in which it is determined whether the combustion mode is the stratified combustion mode or the weak stratified combustion mode. When the answer is No, that is, when the combustion mode is the homogeneous combustion mode, the procedure proceeds to step 105 in which the combustion improve control is not performed to end the routine.
When the answer is Yes in step 102, the procedure proceeds to step 103 in which the combustion variation parameter is compared with a threshold to determine whether the combustion state in any cylinder is deteriorated. When no deterioration of combustion state is detected, the procedure proceeds to step 105 in which the combustion improve control is not performed to end the routine.
When the answer is Yes in step 103, the procedure proceeds to step 104 in which at least one of the combustion improve control (1)-(5) is performed to improve the combustion state.
The present invention can be applied to a system which is not provided with one of the compression stroke injection mode (stratified combustion mode) and the intake-compression divided injection mode (weak stratified combustion mode).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-191509 | Jul 2007 | JP | national |
