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(11) | EP 1 249 600 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Fuel injection control system for internal combustion engine and method |
| (57) Control for injecting fuel is performed both through a first nozzle hole (4) and
a second nozzle hole (5) by setting a needle valve (2) at a high-lift position in
a fuel injector. The fuel injection is performed only through the first nozzle hole
(4), not through the second nozzle hole (5) by setting the needle valve (2) at a low-lift
position of the fuel injector. When operation of an internal combustion engine continues
for a predetermined period of time under conditions requiring the needle valve (2)
to be set in the low-lift position, control for injecting the fuel through the nozzle
hole (5) is performed. |
BACKGROUND OF THE INVENTION
1. Field of the Invention
2. Description of Related Art
[0002] In a known fuel injection control system for an internal combustion engine, fuel injection is allowed both through a first nozzle hole and a second nozzle hole formed in a fuel injection system of the internal combustion engine by setting a nozzle hole opening/closing valve at a first valve position. Meanwhile, in the aforementioned fuel injection control system, the fuel injection is allowed only through the first nozzle hole, but not through the second nozzle hole by setting the nozzle hole opening/closing valve at a second valve position. For example, Japanese Patent Laid-Open No.11-351105 discloses the fuel injection control system for an internal combustion engine of the aforementioned type. In the fuel injection control system, a nozzle hole opening/closing valve is lifted to a high-lift position as the pressure within a hydraulic chamber that urges the nozzle hole opening/closing valve toward a valve closing direction is decreased so as to inject the fuel both through the first nozzle hole and the second nozzle hole. Meanwhile, the nozzle hole opening/closing valve is moved to a low-lift position as the pressure within the hydraulic chamber that urges the nozzle hole opening/closing valve toward the valve closing direction is increased so as to inject the fuel only through the first nozzle hole, but not through the second nozzle hole.
[0003] The Japanese Patent Laid-Open No.11-351105 discloses no description as to how the nozzle hole opening/closing valve is executed when the engine operation continues for a long period of time under conditions requiring the nozzle hole opening/closing valve to be set at the low-lift position. Accordingly, in the aforementioned fuel injection control system, the nozzle hole opening/closing valve may be kept at the low-lift position so long as the engine operation continues under conditions requiring the nozzle hole opening/closing valve to be set at the low-lift position. If the nozzle hole opening/closing valve is kept at the low-lift position, that is, the fuel is not injected through the second nozzle hole for a relatively long period of time, deposits may accumulate in a periphery or inside of an outlet of the second nozzle hole, resulting in clogging.
SUMMARY OF THE INVENTION
[0004] It is an object of the invention to provide a fuel injection control system for an internal combustion engine which prevents clogging of a nozzle hole caused by a longperiod operation of the engine under conditions requiring no fuel injection through the nozzle hole.
[0005] According to an aspect of the invention, a fuel injection control system for controlling a fuel injection system of an internal combustion engine is provided with a nozzle hole opening/closing valve, a first nozzle hole, and a second nozzle hole. The fuel is injected through the first nozzle hole and the second nozzle hole when the nozzle hole opening/closing valve is set at a first position, and the fuel is injected only through the first nozzle hole but not through the second nozzle hole when the nozzle hole opening/closing valve is set at a second position. The fuel injection control system characterized in that control for injecting the fuel through the second nozzle hole is performed when an operation of the internal combustion engine continues for a predetermined period of time under operating conditions requiring the nozzle hole opening/closing valve to be set at the second position.
[0006] According to another aspect of the invention, a control for injecting the fuel through the second nozzle hole is performed when the internal combustion engine is operated for the predetermined period of time under the operating conditions requiring the nozzle hole opening/closing valve to be set at the second position even when no fuel injection through the second nozzle hole is required.
[0007] According to another aspect of the invention, the aforementioned aspects of the invention, when the engine operation continues for a predetermined period of time under conditions requiring the nozzle hole opening/closing valve to be set at the second position, control for injecting the fuel through the second nozzle hole is perfomred. More specifically, when the engine operation continues for the predetermined period of time under conditions requiring the nozzle hole opening/closing valve to be set at the second position, the fuel is forcibly injected through the second nozzle hole even when the fuel injection through the second nozzle hole is not required. This may prevent the nozzle hole opening/closing valve from being kept at the second position, thus preventing the state in which the fuel is not injected through the second nozzle hole for a long period of time. Accordingly, this may avoid clogging of the second nozzle hole caused by deposits accumulated in the periphery or inside of the second nozzle hole resulting from the state in which no fuel injection has been performed for a relatively long period of time.
[0008] According to another aspect of the invention, control for injecting the fuel through the second nozzle hole is performed at such a timing that keeps an output torque of the internal combustion engine unchanged.
[0009] The fuel injection control system according to the aforementioned aspect of the invention may prevent the change in the output torque of the engine caused by the forcible fuel injection through the second nozzle hole under the engine operating conditions requiring no fuel injection through the second nozzle hole.
[0010] According to another aspect of the invention, control for injecting the fuel through the second nozzle hole is performed during an exhaust stroke of the internal combustion engine.
[0011] In the fuel injection control system according to the aforementioned aspect of the invention, control for injecting the fuel through the second nozzle hole is performed during an exhaust stroke of the engine which hardly affects the output torque of the engine. This may prevent the change in the output torque of the engine caused by forcible injection of the fuel through the second nozzle hole under the engine operating conditions requiring no fuel injection through the second nozzle hole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
FIG. 1 is an enlarged view of an essential portion of a fuel injection control system for an internal combustion engine according to an embodiment of the invention;
FIG.2 is an enlarged view of the essential portion of the fuel injection control system showing that a nozzle hole opening/closing valve is lifted by a relatively small lifting amount to be set at a low-lift position;
FIG.3 is an enlarged view of the essential portion of the fuel injection control system showing that the nozzle hole opening/closing valve is lifted by a relatively large lifting amount to be set at a high-lift position;
FIG.4 is a flowchart representing a fuel injection control routine; and
FIG. 5 is a graph that shows a relationship between the lifting amount of the nozzle hole opening/closing valve and the fuel injection amount with respect to the fuel injection pressure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0014] FIG. 1 is an enlarged view of an essential portion of a fuel injection control system for an internal combustion engine according to an embodiment of the invention. Referring to FIG. 1 showing a tip of an injector 1, a needle valve 2 is urged in a valve opening direction (upward direction in FIG.1) to be lifted when electricity is applied to a known solenoid or piezoresistive element (not shown). The needle valve 2 is urged in a valve closing direction (downward direction in FIG.1) by a spring (not shown). The lift amount of the needle valve 2 is kept zero so long as no electricity is applied to the solenoid or the piezoresistive element. When relatively low voltage of electricity is applied to the solenoid or the piezoresistive element, the lift amount of the needle valve 2 becomes relatively small. Meanwhile when relatively high voltage of electricity is applied to the solenoid or the piezoresistive element, the lift amount of the needle valve 2 becomes relatively large. In the embodiment of the invention, the solenoid is employed to lift the needle valve 2. However, the needle valve may be lifted by a hydraulic pressure as disclosed in Japanese Patent Laid-Open No. 11-351105.
[0015] Formed in a nozzle housing 3 are a set of first nozzle holes 4 through which the fuel is injected when the needle valve 2 is lifted, and a set of second nozzle holes 5. When the lift amount of the needle valve 2 is relatively small, that is, the needle valve 2 is set at a low-lift position, the fuel is not injected through the second nozzle holes 5. Meanwhile, when the lift amount of the needle valve 2 is relatively large, that is, the needle valve 2 is set at a high-lift position, the fuel is injected through the second nozzle holes 5. When the fuel injection both through the first nozzle holes 4 and the second nozzle holes 5 is stopped, the needle valve 2 is seated on a first seat portion 6. When the fuel injection through the first nozzle holes 4 is performed and the fuel injection through the second nozzle holes 5 is stopped, the tip of the needle valve 2 fits into a second seat portion 7. Referring to FIG. 1, when the valve lift amount is zero, the needle valve 2 is seated on the first seat portion 6. Therefore, no fuel is injected through the first nozzle holes 4 nor the second nozzle holes 5.
[0016] FIG.2 shows the injector at the low-lift state in which the lift amount of the needle valve 2 is relatively small. In the low-lift state, the needle valve 2 is not seated on the first seat portion 6, and the tip of the needle valve 2 fits into the second seat portion 7. Therefore, the fuel is injected only through the first nozzle holes 4, and is not injected through the second nozzle holes 5. FIG. 3 shows the injector at the high-lift state in which the lift amount of the needle valve 2 is relatively large. In the high-lift state, the needle valve 2 is not seated on the first seat portion 6, and the tip of the needle valve 2 does not fit into the second seat portion 7. Therefore, the fuel is injected both through the first nozzle holes 4 and the second nozzle holes 5.
[0017] As described above, the needle valve 2 is seated on the first seat portion 6. The tip of the needle valve 2 fits into the second seat portion 7, and a small gap is defined by the tip of the needle valve 2 and the second seat portion 7. In the low-lift sate in which the tip of the needle valve 2 fits into the second seat portion 7, the fuel is not injected through the second nozzle holes 5. However, the fuel may infiltrate into the second nozzle holes 5 through the gap between the tip of the needle valve 2 and the second seat portion 7. In the aforementioned state, that is, the needle valve 2 is kept at the low-lift position to prevent fuel injection through the second nozzle holes, deposits may be accumulated in the periphery or inside of the outlet of the second nozzle holes 5, resulting in clogging. The clogging of the second nozzle holes 5, thus, may change the fuel injection quantity or spray characteristics, promote smoke generation, and decrease the output torque of the engine
[0018] FIG.4 shows a flowchart of a fuel injection control executed by the fuel injection control system of the embodiment of the invention. The control routine is executed at a predetermined time interval, for example, at every calculation of a command value for the fuel injection quantity in each stroke. Referring to FIG.4, upon start of the routine, in step 101, it is determined whether a flag indicating an unclogging mode has been turned ON. If the flag indicating the unclogging mode has been turned ON through steps to be described later, YES is obtained in step 101, and the process proceeds to step 110. If the flag indicating the unclogging mode has been turned OFF through steps to be described later, NO is obtained in step 101, and the process proceeds to step 102.
[0019] In step 102, the lift amount of the needle valve 2 is estimated according to a relationship between the fuel injection pressure (common rail pressure) and a fuel injection quantity both calculated in step (not shown) referring to the graph shown in FIG.5. As shown in FIG.5, the more the fuel injection quantity becomes, the larger the lift amount of the needle valve 2 becomes, and the higher the fuel injection pressure becomes, the smaller the lift amount of the needle valve becomes.
[0020] In Step 103 of the flowchart shown in FIG. 4, it is determined whether the engine is operated in the low-lift state as shown in FIG.2 based on the lift amount of the needle valve 2 estimated in step 102. If YES is obtained in step 103, that is, the low-lift operation as shown in FIG.2 is being performed, the process proceeds to step 104. In step 104, a low-lift counter indicating a continuous low-lift operation time, that is, the accumulated amount of deposits in the periphery or inside of the outlet of the second nozzle holes 5 is incremented. Meanwhile, if NO is obtained in step 103, that is, the high-lift operation as shown in FIG.3 is being performed, the process proceeds to step 105. In step 105, the low-lift counter is decremented. Next in step 106, it is determined whether the count of the low-lift counter exceeds a predetermined value. That is, it is determined whether the engine operation continues for a predetermined period of time under the engine operating conditions requiring the needle valve 2 to be set at the low-lift position (refer to FIG.2). If YES is obtained in step 106, the process proceeds to step 107. If NO is obtained in step 106, the routine ends without changing the value of the low-lift counter. In step 107, the flag indicating the unclogging mode is turned ON. Then in step 108, a counter indicating the number of times for performing unclogging is set to FULL. In step 109, the low-lift counter is cleared.
[0021] Meanwhile in step 110, the needle valve 2 is forcibly set to the high-lift position (refer to FIG.3), and the fuel is injected through the second nozzle holes 5 during the exhaust stroke. In the case where it is determined that the engine operation has continued for a predetermined time period under the conditions requiring the needle valve 2 to be set in the low-lift position as shown in FIG. 2 in step 106, and the flag indicating the unclogging mode is turned ON in step 107 in the last control routine shown in FIG. 4, it is determined that the flag indicating the unclogging mode is turned ON in step 101 (YES is obtained). Therefore, the process proceeds to step 110 in which the needle valve 2 is forcibly moved to the high-lift position such that the fuel is injected at a high pressure through the second nozzle holes 5. The fuel injected during the exhaust stroke is oxidized by an HC purification device, for example, an oxidization catalyst, disposed in an exhaust passage of the engine. When the needle valve 2 is set at the high-lift position and the fuel is injected through the second nozzle holes 5 at high pressure, the deposits accumulated in the periphery or inside of the outlet of the second nozzle holes 5 can be forcibly swept away by the injected spray. In the embodiment of the invention, in step 110, the fuel is injected during the exhaust stroke when the needle valve 2 is forcibly set at the high-lift position. However, the needle valve 2 may be forcibly set at the high-lift position at the timing other than the exhaust stroke so as to inject the fuel so long as the output torque of the engine is kept unchanged.
[0022] In step 111, the counter indicating the number of times for unclogging, that represents the necessity of the fuel injection during the exhaust stroke is decremented. Then in step 112, it is determined whether the counter is decremented to zero. If YES is obtained in step 112, that is, the counter is decremented to zero, the process proceeds to step 113. In step 113, the flag indicating the unclogging mode is turned OFF. If NO is obtained in step 112, that is, the counter is not decremented to zero, the control routine ends without executing step 113. In other words, the fuel injection during the exhaust stroke in which the needle valve 2 is forcibly set at the high-lift position is executed at every control routine to be executed until the counter becomes zero from FULL.
[0023] As aforementioned, when it is determined in step 106 that the engine operation has continued for a predetermined time under the engine operating conditions requiring the needle valve 2 to be set at the low-lift position (refer to FIG. 2), the process proceeds to step 110 by which the fuel is forcibly injected through the second nozzle holes 5. More specifically, when it is determined in step 106 that the engine operation has continued for the predetermined time period under the engine operating conditions requiring the needle valve 2 to be set at the low-lift position, the fuel is forcibly injected through the second nozzle holes 5 even when no fuel injection through the second nozzle holes 5 is required. This may prevent the needle valve 2 from being kept at the low-lift position to cut off the fuel injection through the second nozzle holes 5 for a relatively long period of time. The resultant accumulation of deposits in the periphery or inside of the second nozzle holes 5 may be prevented.
[0024] In the aforementioned embodiment, the fuel is forcibly injected through the second nozzle holes 5 at a timing that hardly affects the output torque of the engine. For example, in step 110, the fuel is forcibly injected through the second nozzle holes 5 during the exhaust stroke that hardly affects the output torque of the engine. Even if the fuel injection is forcibly performed through the second nozzle holes 5 under the engine operating conditions requiring no fuel injection through the second nozzle holes 5, the output torque of the engine may be kept unchanged.
[0025] In the aforementioned embodiment, the fuel injection is forcibly performed even when the needle valve has been kept at the second nozzle holes for a relatively long period of time. Therefore, even in the state where no injection through the second nozzle holes has continued for a long period of time, clogging of the second nozzle holes owing to accumulation of deposits in the periphery or inside of the output of the second nozzle holes may be prevented.
[0026] The fuel injection control system of the aforementioned embodiment may prevent the output torque from being changed accompanied with forcible fuel injection through the second nozzle holes under the engine operating conditions requiring no fuel injection through the second nozzle holes.
[0027] Fuel injection is performed both through a first nozzle holes 4 and a second nozzle holes 5 by setting a needle valve 2 at a high-lift position in a fuel injector. The fuel injection is performed only through the first nozzle holes 4, not through the second nozzle holes 5 by setting the needle valve 2 at a low-lift position of the fuel injector. When operation of an internal combustion engine continues for a predetermined period of time under conditions requiring the needle valve 2 to be set in the low-lift position, the fuel injection is forcibly performed through the second nozzle holes 5.
[0028] Control for injecting fuel is performed both through a first nozzle hole (4) and a second nozzle hole (5) by setting a needle valve (2) at a high-lift position in a fuel injector. The fuel injection is performed only through the first nozzle hole (4), not through the second nozzle hole (5) by setting the needle valve (2) at a low-lift position of the fuel injector. When operation of an internal combustion engine continues for a predetermined period of time under conditions requiring the needle valve (2) to be set in the low-lift position, control for injecting the fuel through the nozzle hole (5) is performed.
1. A fuel injection control system for controlling a fuel injection system of an internal
combustion engine, the fuel injection system including a nozzle hole opening/closing
valve (2), a first nozzle hole (4), and a second nozzle hole (5), wherein a fuel is
injected through the first nozzle hole (4) and the second nozzle hole (5) when the
nozzle hole opening/closing valve (2) is set at a first position, and the fuel is
injected only through the first nozzle hole (4) but not through the second nozzle
hole (5) when the nozzle hole opening/closing valve (2) is set at a second position,
the fuel injection control system being characterized in that:
control for injecting the fuel through the second nozzle hole (5) is performed when an operation of the internal combustion engine continues for a predetermined period of time under operating conditions requiring the nozzle hole opening/closing valve (2) to be set at the second position.
2. A fuel injection control system according to claim 1, wherein control for injecting
the fuel through the second nozzle hole (5) is performed when the internal combustion
engine is operated for the predetermined period of time under the operating conditions
requiring the nozzle hole opening/closing valve (2) to be set at the second position
even when no fuel injection through the second nozzle hole is required.
3. A fuel injection control system according to claim 1 or 2, wherein control for injecting
the fuel through the second nozzle hole (5) is performed at such a timing that keeps
an output torque of the internal combustion engine unchanged.
4. A fuel injection control system according to any one of claims 1, 2 and 3, wherein
control for injecting the fuel through the second nozzle hole (5) is performed during
an exhaust stroke of the internal combustion engine.
5. A fuel injection control method for controlling a fuel injection system of an internal
combustion engine, the fuel injection system including a nozzle hole opening/closing
valve (2), a first nozzle hole (4), and a second nozzle hole (5), wherein a fuel is
injected through the first nozzle hole (4) and the second nozzle hole (5) when the
nozzle hole opening/closing valve (2) is set at a first position, and the fuel is
injected only through the first nozzle hole (4) but not through the second nozzle
hole (5) when the nozzle hole opening/closing valve (2) is set at the second position,
the fuel injection control method being characterized in that:
control for injecting the fuel through the second nozzle hole (5) is performed when an operation of the internal combustion engine continues for a predetermined period of time under operating conditions requiring the nozzle hole opening/closing valve (2) to be set at the second position.
6. A fuel injection control method according to claim 5, wherein control for injecting
the fuel through the second nozzle hole (5) is performed when the internal combustion
engine is operated for the predetermined period of time under the operating conditions
requiring the nozzle hole opening/closing valve (2) to be set at the second position
even when no fuel injection through the second nozzle hole (5) is required.
7. A fuel injection control method according to claim 5 or 6, wherein control for injecting
the fuel through the second nozzle hole (5) is performed at such a timing that keeps
an output torque of the internal combustion engine unchanged.
8. A fuel injection control method according to any one of claims 5, 6 and 7, wherein
control for injecting the fuel through the second nozzle hole (5) is performed during
an exhaust stroke of the internal combustion engine.