JPH0647964B2 - Fuel pre-injection control method for diesel engine - Google Patents

Description

The present invention relates to a fuel pre-injection control method for a diesel engine.

[Conventional technology]

In a diesel engine, there is an ignition delay time from the injection of fuel to the occurrence of combustion, during which the fuel supplied to the combustion chamber explosively burns in the early stage of combustion, and the pressure inside the combustion chamber rises sharply. If this pressure rise is too rapid, a knocking sound called a knocking sound peculiar to a diesel engine is generated.
The noise caused by this knocking sound is particularly problematic during low speed and low load operation such as idling. To reduce this knocking sound, the injection rate at the beginning of fuel injection should be lowered to reduce the fuel supply amount from the time the fuel is injected until the time of ignition, and a small amount of fuel that does not ignite prior to the main injection. Is injected in advance to create an atmosphere that is easy to ignite with respect to the main injection to shorten the ignition delay (JP-A-57-658).
No. 52), it is known that the method of making the fuel injection form the preliminary injection (pilot injection) before the main injection and continuing the combustion by the preliminary injection to the combustion by the main injection is effective.

It is also known that the combustion state is alleviated according to these methods, so that the emission amount of nitrogen oxide NO _{X in} the exhaust gas can be reduced.

When the pre-injection is properly performed, NO _X resulting from the fuel injected during the ignition delay period (delay period from injection to ignition) peculiar to the diesel engine burning at the time of ignition
Can be suppressed. In other words, it is important to create a spark from the preliminary injection so that the main injection is gently ignited as soon as the main injection is started.

Therefore, the relationship between the preliminary injection and the main injection is that the preliminary injection is too small to generate a spark or disappear at the start of the main injection, and the spark itself is too large at the start of the main injection. At least three important points are that self-combustion has not occurred and that main injection is started in the presence of the spark.

Japanese Patent Application No. 58-232091 (Japanese Patent Application Laid-Open No. 60-12)
5753) starts the main injection after a lapse of a predetermined time after confirmation of the formation of the fire, and considers the relationship of
It does not consider the relationship between the fire source itself and the cause.

[Problems to be solved by the invention]

The present invention has been made to solve the above-mentioned problems, and the combustion pre-injection of a diesel engine that can always control the fuel injection amount at the time of pre-injection to an optimum injection amount that matches the combustion state of the engine. The purpose is to provide a control method.

[Means for solving problems]

Therefore, in the present invention, the preliminary injection is performed before the main injection,
The feature is that the relationship between the fuel injection start timing of the main injection and the fuel timing of the preliminary injection is determined, and both timings should be matched to control the fuel injection amount during the preliminary injection to change the combustion timing of the preliminary injection. A fuel pre-injection control method for a diesel engine is provided.

[Action]

According to the method of the present invention, the injection amount of the preliminary injection is controlled so as to match the fuel injection start timing of the main injection with the combustion timing of the preliminary injection. It is possible to prevent the combustion from being abruptly burned, or conversely, the amount of injection being too small to obtain the effect of the fire type and the main injection to be abruptly burned.

〔Example〕

An embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a diagram schematically showing the overall configuration of an apparatus for carrying out the method of the present invention. A combustion injection device 3 is provided facing the combustion chamber 2 for each cylinder of the diesel engine body 1. The fuel injection device 3 is a plunger type pressurizing pump 4
And a combustion injection valve 5. The plunger 6 of the pressurizing pump 4 is driven by a cam 8 fixed to a drive shaft 7 that interlocks with the crankshaft of the engine. The pressurizing chamber 9 of the pressurizing pump 4 communicates with the fuel tank 11 via the check valve 10 and also communicates with the fuel injection valve 5 in the fuel injection device 3. The fuel from the fuel tank 11 is pressurized in the pressure chamber 9,
When the pressure exceeds a certain pressure, the nozzle needle 12 of the fuel injection valve 5 is raised to open the fuel injection valve 5 and fuel is injected into the combustion chamber 2. A needle sensor 13 that detects the rise of the nozzle needle 12 is provided in the fuel injection device 3. The needle sensor 13 is, for example, a position detector including a differential transformer, detects the lift amount of the nozzle needle 12, and inputs the signal to an electronic control unit (ECU) 14 equipped with a microcomputer.

The pressurizing chamber 9 communicates with the fuel injection valve 5, and the solenoid valve 1
It is connected to 5. The solenoid valve 15 is a spill valve that opens and closes between the pressurizing chamber 9 and the return pipe 16 connected to the fuel tank 11. When the solenoid valve 15 is driven and the valve is opened,
The high-pressure fuel in the pressurizing chamber 9 overflows into the return pipe 16 and is not injected from the fuel injection valve 5. Therefore, the combustion injection into the combustion chamber 2 can be controlled by opening / closing the solenoid valve 15 at an appropriate timing.

The solenoid valve 15 for causing this overflow is an electronic control unit (E
It is driven by the CU) 14. In addition to the needle lift amount signal from the needle sensor 13 described above, the electronic control unit 14 detects the engine temperature signal from the temperature sensor 17 that detects the temperature of the engine from the cooling water temperature or the oil temperature, and the depression amount of the accelerator pedal. A throttle opening signal from the throttle sensor 18, a rotation speed signal from a rotation speed sensor 19 that detects the rotation angle of the engine, and the like are input, and combustion from a combustion detection sensor 20 that detects ignition combustion in the combustion chamber 2 is performed. The detection signal is input.

The combustion detection sensor 20 is a pressure sensor provided facing the combustion chamber 2, and detects combustion when the pressure in the combustion chamber 2 rapidly increases due to ignition. Although a pressure sensor is used as the combustion detection sensor 20 in this embodiment, it is also possible to detect combustion using an optical sensor.

In the electronic control unit (ECU) 14, each sensor (1
3, 17, 18, 19, 20), it is determined whether or not the preliminary injection should be performed, and the solenoid valve 15 is opened / closed at an appropriate timing, and the fuel injection amount and the injection in the preliminary injection and the main injection are performed. The timing is controlled so that it becomes a value suitable for the operating condition of the engine.

FIG. 2 is a timing chart showing a case where the preliminary injection is executed.

The solenoid valve 15 is closed at time t1 and opened at time t2 in synchronization with the pressing of the plunger 6 of the pressurizing pump 4. Then, again, it is closed at time t3, and at time t4.
Open to. When the solenoid valve 15 is closed at time t1, the fuel cannot overflow and the fuel pressure in the pressurizing chamber 9 rises. As the fuel pressure rises, the nozzle needle 12 of the combustion injection valve 5 rises, the fuel injection valve 5 opens and pre-injection starts. When the solenoid valve 15 is opened at time t2, the fuel overflows, the fuel pressure in the pressurizing chamber 9 decreases, the nozzle needle 12 descends, the injection valve 5 closes, and the preliminary injection ends. Similarly, the main injection is started from time t6 by closing the solenoid valve 15 at time t3, and the main injection is ended by opening the solenoid valve 15 at time t4.

As described above, the fuel injection amount in the preliminary injection and the main injection is
Times (t2-t5) and (t4-t4) from when the nozzle needle 12 starts rising to when the solenoid valve 15 is opened, respectively.
t6).

Further, the times t5 and t6 when the nozzle needle 12 starts to move upward and the fuel injections of the preliminary injection and the main injection are started,
The closing times t1 and t3 of the solenoid valve 15 are controlled so that the top dead center of each cylinder has a predetermined phase depending on the engine state such as the engine speed, temperature, and load.

Then, the combustion start duration t7 is detected by the combustion detection signal from the combustion detection sensor 20, and the valve opening time t2 of the solenoid valve 15 is controlled so that the combustion start time t7 matches the main injection start time t6. By controlling the fuel injection amount at the time of injection, the combustion by the preliminary injection can be smoothly continued to the combustion by the main injection.

Electronic control unit (ECU) 1 for executing the above-mentioned control concept
Regarding the actual processing by the microcomputer in 4,
Description will be made with reference to the flowcharts shown in FIGS. 3 and 4.

When the power is turned on and the processing is started, first, step 1
At 01, initialization such as initialization of the memory (RAM) in the microcomputer is performed. Next, at step 102, it is checked whether or not the engine startup is completed, and if it is not completed, the startup injection processing routine 200 is started.
Proceed to. In the startup injection processing routine, the injection processing is performed with the fixed fuel injection amount and injection timing, and the process returns to step 102. On the other hand, if the start of the engine is completed, the routine proceeds to step 103.

In step 103, the engine speed Ne, the throttle opening, and the engine temperature T are read.

Next, at step 104, it is checked from the rotational speed Ne and the throttle opening whether or not the engine is idling,
Next, at step 105, the engine temperature T is a predetermined value T
It is checked whether it is O or more. Whether or not the engine is idling is determined from the fact that the throttle opening is 0% and the rotation speed is, for example, 900 rotations or less (Ne ≦ 900 rpm). Further, the predetermined value TO of the temperature is, for example, 0
Set to ° C.

If the engine is not idling or the engine temperature is not equal to or higher than the predetermined value, it is determined that the operating state of the engine is not in the pre-injection execution region, the process proceeds to step 106, the pre-injection execution flag is reset, and then the load operation is performed. The process proceeds to the injection processing routine 300. In this load operation injection processing routine 300, injection is performed only by normal main injection,
No preliminary injection is performed.

On the other hand, when it is determined in steps 104 and 105 that the engine is idling and the engine temperature is equal to or higher than the predetermined value, it is determined that the operating state of the engine is in the preliminary injection execution region, and the process proceeds to step 107. .

In step 107, the preliminary injection execution flag is set and the routine proceeds to the preliminary injection processing routine 400.

FIG. 4 is a flowchart showing the processing in the preliminary injection processing routine 400.

In the preliminary injection processing routine 400, first, step 401
At, the valve closing times t1 and t3 of the solenoid valve 15 that determine the start times of the preliminary injection and the main injection are calculated. This calculation is based on the engine speed Ne and the engine temperature T, and the memory (R
This is done by retrieving the two-dimensional map stored in OM).

Next, in step 402, the preliminary injection time C from the start of the preliminary injection to the opening of the solenoid valve 15 is calculated.
This preliminary injection time C is determined by the engine speed Ne and the engine temperature T.
Is calculated by the calculation formula stored in the memory (ROM).

Next, at step 403, the correction value ΔC is added to the preliminary injection time C to obtain the final preliminary injection time D. The correction value ΔC is set to 0 as an initial value.

Then, in step 404, the needle lift valve opening time t5 at the start time of the preliminary injection is read, and in the next step 405, whether the final preliminary injection time D previously obtained from the valve opening time t5 has elapsed. Find out. When the time D has elapsed, the routine proceeds to step 406, where the solenoid valve 15 is opened and the preliminary injection is ended.

Next, at step 407, the valve opening time t6 of the nozzle needle 12 at the time when the main injection is started and the combustion start time t7 are read.

Then, at step 408, the valve opening time t6 of the nozzle needle 12 is compared with the combustion start time t7, and if the combustion start time t7 is later, it is determined that the preliminary injection amount is smaller,
In the next step 409, the minimum value 1 is added to the correction value ΔC to correct the next preliminary injection amount. On the other hand, as shown in FIG. 2, if the combustion start time t7 is earlier than the nozzle needle opening time t6, it is determined that the preliminary injection amount was excessive, and the minimum value 1 is subtracted from the correction value ΔC in the next step 410. To correct the next preliminary injection amount.

The pre-injection processing routine 400 is ended in the above steps, the process returns to step 103 again, and the above-described processing is repeatedly executed.

In this way, the preliminary injection is controlled so that the combustion start time t7 is always near the main injection start time t6, and the combustion by the preliminary injection can smoothly transition to the combustion of the main injection fuel.

〔The invention's effect〕

As described above, according to the present invention, the fuel injection amount at the time of pre-injection can always be controlled to the optimum injection amount that matches the combustion state of the engine. Since it can be managed, there is an excellent effect that the combustion state from the preliminary injection to the main injection can be made gentle.

[Brief description of drawings]

The drawings show one embodiment of the present invention, FIG. 1 is an overall configuration diagram of an apparatus for carrying out the present invention, FIG. 2 is a timing chart showing preliminary injection, and FIGS. 3 and 4 are processes of an electronic control unit. It is a flowchart showing. 1 ... Engine body, 2 ... Combustion chamber, 4 ... Pressurizing pump, 5
... Fuel injection valve, 6 ... Plunger, 9 ... Pressurizing chamber, 1
2 ... Nozzle needle, 13 ... Needle sensor, 14
… Electronic control device, 15… Solenoid valve (spill valve), 20…
… Combustion detection sensor.

Claims (1)

[Claims] 1. A fuel injection amount at the time of preliminary injection, in which preliminary injection is executed before the main injection, the relationship between the fuel injection start timing of the main injection and the fuel timing of the preliminary injection is determined, and both timings should be matched. Is controlled to change the combustion timing of the pre-injection.