JP4784571B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device for a diesel engine.

  In a diesel engine, pilot injection for injecting a small amount of fuel is performed prior to main injection, which is main fuel injection, for the purpose of improving the combustion state of fuel in a combustion chamber. Since pilot injection is very small compared to the amount of fuel injected in main injection, it is necessary to precisely control the fuel injected from the injector. Therefore, a fuel injection control device that learns a small amount of fuel injection that can be injected from an injector has been proposed (see Patent Documents 1 and 2).

In Patent Document 1, during idling operation of a diesel engine, fuel necessary for maintaining idling is divided into n times and injected. By dividing the fuel injection amount into n times, a small amount of fuel injection amount is learned from the difference between the rotational speed of the diesel engine and the target rotational speed while reducing the fuel per injection. Moreover, in patent document 2, after adjusting the fuel injection amount in main injection between the cylinders of a diesel engine, the fuel injection amount in pilot injection is adjusted.
JP 2005-320964 A JP 2005-248739 A

  However, for example, in the case of a large diesel engine mounted on a large vehicle, the amount of fuel injection required to maintain idling increases. Therefore, when the fuel required for idling is divided into n times and injected as in Patent Document 1, the fuel injection amount per time becomes large. When learning a small amount of fuel injection, it is desirable that the amount of fuel injected from the injector is as small as possible. That is, it is desirable to learn the minimum amount of fuel that can be injected from the injector. On the other hand, there is a limit to the period during which fuel can be injected from the injector at a predetermined injection timing. As a result, in the case of a large diesel engine with a large fuel injection amount per time, it is difficult to reduce the fuel injection amount per time due to an increase in the number of injections. In Patent Document 2, after adjusting only the main injection, the main injection is adjusted to include pilot injection. Therefore, during the operation of the diesel engine, the fuel injection pattern only for main injection and the fuel injection pattern consisting of pilot injection and main injection are switched. As a result, there is a problem that when the fuel injection pattern is switched, a change in combustion noise or a change in generated torque is caused, and the drivability of the diesel engine is deteriorated.

  Accordingly, the present invention has been made in view of the above problems, and its purpose is to learn a small amount of fuel injection from an injector regardless of the displacement of a diesel engine without deteriorating drivability. An object of the present invention is to provide a fuel injection control device to be implemented.

  In the first aspect of the present invention, the injection pattern setting means sets an injection pattern composed of divided pilot injection obtained by dividing main injection and pilot injection into n times. When learning a small amount of injection in pilot injection, the pilot injection amount reduction means gradually reduces the injection amount per time in divided pilot injection for each combustion stroke. The rotation change means detects a change in the rotation of the diesel engine accompanying a decrease in the injection amount in the divided pilot injection. When the amount of fuel injected from the injector is gradually reduced, the fuel injection disappears after a certain period. The injection amount immediately before the fuel injection disappears becomes the minimum amount of fuel injected from the injector, that is, the lower limit value. At this time, since the number of divided pilot injections is set to n in advance, there is no increase in the number of injections and an increase in the amount of fuel per injection. On the other hand, when the fuel injection disappears, a change occurs in the rotation of the diesel engine. Therefore, the pilot injection amount increasing means increases the injection amount per time in the divided pilot injection when a change occurs in the rotation of the diesel engine. As a result, the diesel engine is maintained in stable operation. Therefore, a small amount of fuel injection from the injector can be learned regardless of the exhaust amount of the diesel engine without deteriorating drivability.

  In the invention according to the second aspect, the injection amount of a small amount of fuel injected from the injector is learned for each cylinder of the diesel engine. Therefore, it is possible to learn a small amount of fuel injection from the injector regardless of individual differences among the injectors among the cylinders or changes over time.

Hereinafter, a fuel injection device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing a fuel injection system to which a fuel injection control device according to an embodiment of the present invention is applied. In the present embodiment, the fuel injection control device 10 is applied to a diesel engine 21 in which fuel injection is controlled by a common rail fuel injection system 20. The fuel injection system 20 includes a fuel tank 22, a suction amount control valve 23, a supply pump 24, a common rail 25, and an injector 40. The fuel injection control device 10 includes an engine control device (hereinafter referred to as “ECU: Engine Control Unit”) 11 and an electronic drive device (hereinafter referred to as “EDU: Electronic Drive Unit”) 12. The suction amount control valve 23 and the supply pump 24 constitute an integral pump unit 27.

  The fuel tank 22 stores normal pressure fuel. The fuel inside the fuel tank 22 is supplied to the intake amount control valve 23 via the intake pipe portion 31 by a low-pressure pump (not shown). The supply pump 24 pressurizes fuel sucked into a pressurizing chamber (not shown) by reciprocating a plunger (not shown). In the supply pump 24, the flow rate of the discharged fuel changes according to the flow rate of the fuel sucked into the pressurizing chamber. The plunger receives driving force from a crankshaft 28 of the diesel engine 21. The fuel pressurized by the supply pump 24 is discharged to the common rail 25. A fuel pipe portion 32 is connected to the discharge side of the supply pump 24. The fuel pipe portion 32 connects the supply pump 24 and the common rail 25.

  The common rail 25 is connected to the fuel pipe portion 32 and stores the fuel pressurized by the supply pump 24 in a pressure accumulation state. An injector 40 that injects fuel into each cylinder 29 of the diesel engine 21 is connected to the common rail 25. The injector 40 is provided for each cylinder 29. The fuel stored in the common rail 25 in an accumulated state is injected from the injector 40 into the combustion chamber formed in each cylinder 29. A reflux piping section 33 is connected to the supply pump 24, the common rail 25, and the injector 40. Surplus fuel in the supply pump 24, the common rail 25, and the injector 40 is returned to the fuel tank 22 via the return piping section 33.

  ECU11 and EDU12 are comprised by the microcomputer which has CPU, ROM, and RAM, for example. The CPU controls the entire fuel injection system 20 according to a computer program stored in the ROM. In the ECU 11, a pressure sensor 13, an accelerator sensor 14, a rotation sensor 15 and the like are connected to a circuit on the input side. The pressure sensor 13 is provided on the common rail 25. The pressure sensor 13 detects the pressure of the fuel stored in the common rail 25.

  The pressure sensor 13 outputs the detected fuel pressure in the common rail 25 to the ECU 11 as an electrical signal. The accelerator sensor 14 outputs the depression amount of an accelerator pedal (not shown) to the ECU 11 as an electric signal. The rotation sensor 15 detects the rotation of the crankshaft 28 of the diesel engine 21. The rotation sensor 15 outputs the detected rotation of the crankshaft 28 to the ECU 11 as an electrical signal.

  The ECU 11 detects the operating state of the diesel engine 21 from, for example, an electrical signal related to the rotational state of the diesel engine 21 detected by the rotation sensor 15 and an accelerator pedal depression amount detected by the accelerator sensor 14. The ECU 11 sets the injection amount of fuel injected from the injector 26 according to the detected operating state of the diesel engine 21. The ECU 11 sets the fuel pressure required in the common rail 25 based on the set fuel injection amount.

  In the ECU 11, an intake amount control valve 23, an EDU 12, and the like are connected to a circuit on the output side. The intake amount control valve 23 controls the flow rate of fuel supplied to the supply pump 24 based on the control current output from the ECU 11. The EDU 12 is connected to the electromagnetic valve 41 of the injector 40. The EDU 12 outputs a pulsed drive signal to the electromagnetic valve 41 of the injector 40 based on the drive signal output from the ECU 11. In the injector 40, the solenoid valve 41 is driven based on the pulse-shaped drive signal output from the EDU 12, and fuel injection is intermittently performed. As a result, the injector 40 injects the fuel stored in the common rail 25 into the combustion chamber formed in each cylinder 29 of the diesel engine 21.

A storage unit 16 is connected to the ECU 12. The storage unit 16 has a nonvolatile storage device such as an EEPROM (Electrical Erasable Programmable Read Only Memory). The storage unit 16 stores data used by the ECU 12, computer programs executed by the ECU 11, and the like. The storage unit 16 may be shared with the ROM or RAM of the ECU 11.
The ECU 11 constitutes an injection pattern setting means, a pilot injection amount decreasing means, and a pilot injection amount increasing means in the claims. Further, the ECU 11 constitutes a rotation change detection means in the claims together with the rotation sensor 15.

Next, the operation of the fuel injection control device 10 having the above configuration will be described.
(Fuel injection pattern)
The fuel injection control device 10 sets a normal injection pattern and a divided pilot injection pattern as fuel injection patterns from the injector 40 as shown in FIG. The normal injection pattern is composed of one pilot injection and main injection following the pilot injection. The fuel injection amount in the main injection is set larger than that in the pilot injection. The divided pilot injection pattern is composed of divided pilot injection divided into a plurality of times and main injection following the divided pilot injection. The divided pilot injection is a part of the total injection amount in the normal injection pattern that is divided into n times. The split pilot injection amount Q per split in the split pilot injection is set by the ECU 11 according to the operating state of the diesel engine 21. Note that the initial value of the divided pilot injection amount Q per divided pilot injection can be set to the design value of the minimum injection amount, and the total injection amount in the normal injection pattern and the total injection amount in the divided pilot injection pattern are: It is set so that it is almost the same value.

(Fuel injection)
The ECU 11 outputs a pulsed drive signal to the electromagnetic valve 41 of the injector 40 via the EDU 12. The amount of fuel injected from the injector 40 is controlled by the valve opening time of the electromagnetic valve 41 of the injector 40, that is, the pulse width of the drive signal. The amount of fuel injected from the injector 40 increases as the pulse width of the drive signal becomes longer as shown in FIG. When the diesel engine 21 has a plurality of cylinders 29, one injector 40 is attached to each cylinder 29. Therefore, for example, in the case of a four-cylinder diesel engine 21, four injectors 40 are provided. The injectors 40 attached to each cylinder 29 have different fuel injection characteristics due to individual differences. Therefore, as shown in FIG. 3, the relationship between the amount of fuel injected from the injector 40 and the pulse width of the drive current is different for each injector 40.

  Due to electrical and mechanical characteristics, the solenoid valve 41 of the injector 40 does not operate until the pulse width of the drive signal reaches a predetermined value even when a pulse of the drive signal is applied. In this case, the electromagnetic valve 41 of the injector 40 is activated, and the minimum pulse width of the drive signal from which the fuel is injected from the injector 40 corresponds to the pulse width when the fuel injection amount from the injector 40 is minimum.

(Learning of micro injection amount)
A procedure for learning a minute injection amount by the fuel injection device having the above-described configuration will be described with reference to FIG. The learning of the small amount of injection is performed for each injector 40 provided in each cylinder of the diesel engine 21.
When the ECU 11 reaches a predetermined timing during operation of the diesel engine 21, the ECU 11 proceeds to a routine for learning a small amount of injection. When the routine proceeds to a routine for learning micro injection, the ECU 11 determines whether or not a condition for performing the divided pilot injection is satisfied (S101). The ECU 11 detects whether the diesel engine 21 is in a stable idling state. For example, when the depression amount of the accelerator pedal detected by the accelerator sensor 14 is “0” and the rotational speed of the diesel engine 21 detected by the rotation sensor 15 is a preset idling rotational speed, the ECU 11 Is determined to be in an idling state. When the idling state of the diesel engine 21 continues for a predetermined period, the ECU 11 determines that the diesel engine 21 is in a stable idling state. In addition, ECU11 is good also as a structure which detects the driving | running state of the diesel engine 21 from not only the depression amount of the accelerator pedal and the rotation speed of the diesel engine 21, but a throttle opening degree, a cooling water temperature, or other various sensors of a vehicle, for example. .

  When the ECU 11 determines in step S101 that the condition for performing the divided pilot injection is satisfied, the ECU 11 determines whether or not the divided pilot injection amount Q is stored in the previous routine (S102). The ECU 11 stores the divided pilot injection amount Q learned for each routine in the storage unit 16. Therefore, the ECU 11 determines whether or not the storage unit 16 stores the divided pilot injection amount Q. On the other hand, if the ECU 11 determines in step S101 that the condition for performing the divided pilot injection is not satisfied, the ECU 11 proceeds to step S111 and performs fuel injection according to the normal injection pattern.

When the ECU 11 determines that the divided pilot injection amount Q is stored in step S102, the ECU 11 reads the divided pilot injection amount Q stored in the previous routine from the storage unit 16 (S103). On the other hand, when the ECU 11 determines in step S103 that the divided pilot injection amount Q is not stored, the ECU 11 proceeds to the next step without reading the divided pilot injection amount Q in step S103.
When the ECU 11 reads the divided pilot injection amount Q in step S103, the ECU 11 detects a rotational deviation between the plurality of cylinders 29 of the diesel engine 21 (S104). Further, even when the divided pilot injection amount Q is not stored and the process of step S103 is omitted, the ECU 11 proceeds to step S104 and detects the rotational deviation between the cylinders 29.

  The ECU 11 detects the rotation angle of the crankshaft 28 from the rotation sensor 15. At this time, the rotation angle of the crankshaft 28 per unit time corresponds to the rotation speed of the crankshaft 28. When a plurality of cylinders 29 are provided in the diesel engine 21, the rotation speed of the crankshaft 28 is increased every time fuel is burned in each cylinder 29 as shown in a period t 1 in FIG. growing. Therefore, the rotational speed of the crankshaft 28 periodically changes within a predetermined range corresponding to the combustion in each cylinder 29. At this time, if the fuel is uniformly burned in each cylinder 29, the difference in the rotational speed of the crankshaft 28 between the cylinders 29, that is, the rotational deviation of the crankshaft 28 becomes small.

On the other hand, when fuel is not injected from the injector 40 in any one of the plurality of cylinders 29, the fuel is not burned in the cylinder 29. Therefore, in the period corresponding to the combustion stroke of the cylinder 29 where fuel is not injected, the rotational speed of the crankshaft 28 decreases as indicated by a period t2 in FIG. As a result, the rotational deviation between the plurality of cylinders 29 increases.
When detecting the rotation deviation between the cylinders 29, the ECU 11 determines whether or not the detected rotation deviation is smaller than a predetermined threshold D (S105). When the rotational deviation between the cylinders 29 is smaller than the threshold value D, there is no shortage in the amount of fuel injected from the injector 40 into each cylinder 29 of the diesel engine 21. Therefore, it is determined that the divided pilot injection amount Q set in the previous routine is an amount that can be injected from the injector 40.

Therefore, when the ECU 11 determines that the rotational deviation is smaller than the threshold value D in step S105, the ECU 11 reduces the predetermined pilot amount α from the split pilot injection amount Q set in the previous routine, and sets a new split pilot injection amount Q. (S106). Then, based on the set new divided pilot injection amount Q, fuel is injected from the injector 40 (S107).
On the other hand, when the rotational deviation between the cylinders 29 is larger than the threshold value D, the amount of fuel injected from the injector 40 is insufficient in any cylinder 29 of the diesel engine 21. Therefore, it is determined that the divided pilot injection amount Q set in the previous routine is an amount that cannot be injected from the injector 40, that is, a lower limit value that can be injected from the injector 40.

Therefore, when the ECU 11 determines that the rotational deviation is larger than the threshold value D in step S105, the ECU 11 increases the predetermined pilot β by the divided pilot injection amount Q set in the previous routine of the diesel engine 21 (S121). When the divided pilot injection amount Q is equal to or less than the lower limit value that can be injected from the injector 40, it is difficult for the diesel engine 21 to continue stable operation. Therefore, the ECU 11 adds the predetermined amount β to the divided pilot injection amount Q and resets the divided pilot injection amount.
When the ECU 11 sets a new split pilot injection amount Q in steps S106 and S121, the ECU 11 performs fuel injection from the injector 40 to each cylinder 29 of the diesel engine 21 in accordance with the set split pilot injection amount Q (S107). . At the same time, the ECU 11 writes the set divided pilot injection amount Q in the storage unit 16 (S108).

  In the above-described learning of the minute injection amount, as shown in FIG. 6, the fuel amount in the divided pilot injection, that is, the divided pilot injection amount Q is gradually reduced at every fuel injection timing, that is, every combustion stroke. When the rotational deviation between the cylinders 29 becomes larger than the predetermined threshold D due to the reduction of the divided pilot injection amount Q, the fuel injection amount of the injector 40 provided in the cylinder 29 in which the rotational speed of the crankshaft 28 has decreased. It is determined that the value is below the lower limit.

  If the injection sequence shown in FIG. 5 is an example of a four-cylinder engine in which the first cylinder (# 1) → the third cylinder (# 3) → the fourth cylinder (# 4) → the second cylinder (# 2), the rotational deviation is In the small period t1, the first cylinder (# 1), the third cylinder (# 3), the fourth cylinder (# 4), and the second cylinder (# 2) burn the fuel in order without significantly affecting the rotational speed. Has been done. However, during the period t2, there is a rotational deviation between the fourth cylinder (# 4) and the other first cylinder (# 1), the third cylinder (# 3), and the second cylinder (# 2). At this time, in the fourth cylinder (# 4), it is considered that the divided pilot injection amount Q is equal to or less than the lower limit value of the fuel injected from the injector 40.

  At this time, it is considered that the injector 40 of the fourth cylinder (# 4) cannot inject fuel at the divided pilot injection amount Q or less. Therefore, the ECU 11 learns the divided pilot injection amount Q at this time as the lower limit value of the trace fuel injection amount in the fourth cylinder (# 4). By performing such a decrease in the divided pilot injection amount Q for each injector 40 independently, the ECU 11 sets the lower limit value of the minute fuel injection amount for each injector 40 provided in each cylinder 29 of the diesel engine 21. learn.

In the embodiment described above, the lower limit value of the injection amount at which fuel is not injected from the injector 40 is detected by gradually decreasing the divided pilot injection amount Q. By learning the lower limit value of the detected injection amount for each injector 40, the individual difference in the lower limit value of the fuel injection amount for each injector 40 and the change over time of the fuel injection amount are acquired. Therefore, a minute amount of fuel injection from the injector 40 can be precisely controlled according to individual differences of the injector 40 and changes with time.
Further, in one embodiment, only the divided pilot injection amount Q is reduced without changing the number of pilot injections. Therefore, the lower limit value of the fuel injection amount from the injector 40 is detected without being limited by the fuel injection amount and the fuel injection period. Therefore, a small amount of fuel injection amount from the injector 40 can be learned regardless of the exhaust amount of the diesel engine 21.

  Furthermore, in one embodiment, when a difference occurs in the rotation of the crankshaft 28 due to the combustion of fuel in any one of the plurality of cylinders 29 of the diesel engine 21, the divided pilot of the fuel injected into the cylinder 29 The injection amount Q is increased. Therefore, the lower limit value of the fuel injection amount from the injector 40 is detected without affecting the combustion of the other cylinders 29. Therefore, the influence on the drivability of the diesel engine 21 can be reduced.

In the embodiment of the present invention described above, the four-cylinder diesel engine 21 has been described as an example. However, the number of cylinders 29 of the diesel engine 21 is not limited to four as a matter of course, and can be set arbitrarily.
The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

The schematic diagram which shows schematic structure of the fuel-injection control apparatus by one Embodiment of this invention. Schematic showing the injection pattern of fuel injected from the injector Schematic diagram showing the relationship between the pulse width of the drive signal and the fuel injection amount for each cylinder injector Schematic which shows the flow of control by the fuel-injection control apparatus by one Embodiment of this invention. Schematic showing changes in the rotational speed of a diesel engine The schematic diagram which shows the change of the division | segmentation pilot injection amount for every cylinder in the diesel engine by 1st Embodiment of this invention.

Explanation of symbols

  In the drawings, 10 is a fuel injection control device, 11 is an ECU (injection pattern setting means, pilot injection amount reduction means, rotation change detection means, pilot injection amount increase means), 15 is a rotation sensor (rotation change detection means), and 21 is A diesel engine, 29 is a cylinder, and 40 is an injector.

Claims (2)

In a diesel engine system including an injector for injecting fuel into a combustion chamber formed in a cylinder of a diesel engine, fuel injection from the injector is controlled, and main fuel for combustion is supplied during a single combustion stroke in the combustion chamber. A fuel injection control device that performs main injection to be injected and pilot injection to inject a smaller amount of fuel than the main injection prior to the main injection,
When it is detected that the diesel engine system has shifted to a predetermined operation state, the pilot injection is divided into n injections having the same injection amount, and an injection pattern is set that includes n divided pilot injections and main injections. Setting means;
A pilot injection amount reduction means for gradually reducing the injection quantity per injection in the divided pilot injection set by the injection pattern setting means uniformly for each of the divided n pilot injections;
A rotation change detecting means for detecting a change in rotation of the diesel engine;
When a change in the rotation of the diesel engine is detected by the rotation change detecting means as the injection quantity is reduced in the divided pilot injection by the pilot injection quantity reducing means, the injection quantity per one injection in the divided pilot injection is determined. A pilot injection amount increasing means for quantitatively increasing ,
A fuel injection control device that learns an injection amount per injection in the divided pilot injection in which a change in the rotation of the diesel engine is detected as a lower limit value of a small amount of fuel injected from the injector .   The diesel engine has a plurality of the cylinders, and a reduction in injection amount in the split pilot injection by the pilot injection amount reduction means for each cylinder, detection of a change in rotation of the diesel engine by the rotation change detection means, and 2. The fuel injection control device according to claim 1, wherein an increase in the injection amount in the divided pilot injection is performed by the pilot injection amount increasing means.

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