JP2003074403A - Control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable burning condition when a fuel pressure (rail pressure) in a common rail fluctuates. SOLUTION: An actual rail pressure Prail is detected (S1) and is compared with a target rail pressure Pm (S4, S8) determined in response to the operating condition of an engine (S3). If the absolute value of the difference between the actual pressure Prail and the target rail pressure Pm reaches a prescribed value ΔP or more, pilot injection is divided into two times (S5, S9). In addition, a total quantity of injection by the pilot injection is increased, and a quantity of injection by main injection is decreased (S6, S10). Furthermore, if the actual rail pressure Prail exceeds the target rail pressure Pm by the prescribed value ΔP or more, the maximum lift of a needle valve of an injector is lowered (S7).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine control device including a common rail fuel injection device.

[0002]

2. Description of the Related Art As a conventional diesel engine control device, a device disclosed in Japanese Patent Application Laid-Open No. 2000-97077 is ignited by dividing pilot injection performed prior to main injection into a plurality of times when the engine is started. Performance is improved, while normal warm-up is switched to normal pilot injection without delay after completion, warm-up is completed when the fuel injection amount that increases or decreases by feedback control of idle speed falls below a specified value. Therefore, the pilot injection is switched to the normal one time.

In other words, in the prior art described in the above publication, when the fuel injection amount set by the feedback control of the idle speed exceeds the predetermined value from the start to the warm-up, the combustion is deteriorated. Therefore, the pilot injection is divided into a plurality of times.

[0004]

In recent years, a common rail type fuel injection device has become popular as a fuel injection device for a diesel engine. This is a structure in which high-pressure fuel that is pressure-fed from a supply pump and accumulated in a common rail is injected from an injector. As a method of maintaining the fuel pressure in the common rail at a predetermined pressure,
It is roughly divided into one that controls the amount of fuel pumped from the supply pump and one that controls the amount of fuel that is bypassed from the common rail to the low-pressure piping side (however, there are some that use a combination of both). In either method, the fuel pressure in the common rail is maintained at a predetermined pressure by the balance between the pumping amount or the bypass amount and the fuel injection amount and the overflow flow rate from the injector.

At the time of starting a diesel engine using such a common rail type fuel injection device, until the fuel pressure in the common rail is maintained at a predetermined value,
Fuel pressure in the common rail often causes overshoot and undershoot. This is because fuel is continuously pumped from the supply pump until the pressure reaches almost a predetermined value at the start of cranking, while fuel injection from the injector is started in the middle of it and fuel flowing out from the common rail as the engine speed increases. This is because the amount changes abruptly. In particular, under low temperature conditions, the viscosity and density of the fuel, the timing from the initial explosion to the complete explosion of the engine, etc. are not always stable, so the control pressure may cause overshoot and undershoot. It is difficult to completely suppress it.

FIG. 11 schematically shows the behavior at the time of starting the diesel engine when the fuel pressure (rail pressure) in the common rail changes in this way. If the rail pressure rises excessively (A), the penetration force of the spray becomes strong, and as a result, the amount of the fuel adhering to the wall surface of the combustion chamber increases, and the evaporation of fuel slows down, which may cause unstable combustion. .

On the contrary, when the rail pressure is excessively decreased (B), the spray particle size becomes large and the evaporation rate becomes slow, so that the combustion may become unstable. Here, in the prior art described in the above publication, when the fuel injection amount by the feedback control of the idle speed exceeds a predetermined value, it is determined that warm-up is insufficient (combustion deterioration), and pilot injection is performed a plurality of times. Although it is an attempt to improve combustion, the judgment of deterioration of combustion is due to the order of the decrease of the instantaneous engine speed → the increase of the fuel injection amount → the judgment by the threshold value. However, in the case of the deterioration of combustion due to the fluctuation of the rail pressure as described above, there is a problem that the improvement effect of combustion cannot always be obtained effectively.

In view of the above conventional problems, the present invention provides a diesel engine control device capable of obtaining a stable combustion state by a plurality of pilot injections without delaying the determination of combustion deterioration. The purpose is to

[0009]

Therefore, in the invention of claim 1, in the diesel engine equipped with the common rail fuel injection device, the target rail pressure which is the target value of the fuel pressure in the common rail is set in accordance with the engine operating state. The means for setting, the means for detecting the actual rail pressure, which is the actual value of the fuel pressure in the common rail, and the main injection when the absolute value of the difference between the actual rail pressure and the target rail pressure becomes a predetermined value or more. Means for dividing pilot injection performed in advance into a plurality of times.

According to the second aspect of the invention, when the absolute value of the difference between the actual rail pressure and the target rail pressure exceeds a predetermined value, the total injection amount in the pilot injection is increased and the injection in the main injection is performed. It is characterized by reducing the amount. According to the invention of claim 3, when the actual rail pressure exceeds the target rail pressure by a predetermined value or more, the needle valve maximum lift amount of the injector is reduced.

According to the fourth aspect of the present invention, when the actual rail pressure exceeds the target rail pressure by a predetermined value or more, among the pilot injections of a plurality of times, the earlier pilot injection,
The feature is that the pilot injection amount is reduced. According to the invention of claim 5, when the actual rail pressure is lower than the target rail pressure by a predetermined value or more, among the plurality of pilot injections,
With respect to the first pilot injection, its injection timing is advanced and its injection amount is increased with respect to other pilot injections.

[0012]

According to the first aspect of the present invention, when the absolute value of the difference between the actual rail pressure and the target rail pressure becomes equal to or greater than a predetermined value, the pilot injection is divided to change the engine speed. It is possible to maintain a stable combustion state without delaying the determination of deterioration of combustion because the pilot injection is divided by detecting a change in rail pressure instead of a change in fuel injection amount. .

Further, even if the actual rail pressure is too low, by dividing the pilot injection, it is possible to increase the area in contact with the air in the combustion chamber which has been compressed and has increased in temperature, so that the evaporation of the fuel spray is promoted. Since the fuel of the pilot injection generates heat by the oxidation reaction before the main injection, the fuel of the main injection can be burned quickly.

Further, when the actual rail pressure rises too much, the pilot injection can be divided to weaken the penetration force of each pilot injection, so that the deterioration of the ignitability due to the adhesion to the wall surface can be suppressed. it can. According to the invention of claim 2, by increasing the total injection amount in the pilot injection together with the division of the pilot injection, it is possible to increase the amount of fuel that evaporates before the main injection and reaches the oxidation reaction. The effect of promptly burning the fuel of the main injection can be enhanced.

According to the third aspect of the invention, when the rail pressure rises excessively, the injected fuel adheres to the wall surface and is less likely to evaporate. However, by suppressing the lift amount of the needle valve, the penetration of the spray can be achieved. Since the force is weakened, it is possible to prevent the fuel from adhering to the wall surface and prevent the deterioration of combustion due to the delay of evaporation. According to the invention of claim 4, when the rail pressure rises excessively, the fuel injected at the time when the piston is moving upward and the temperature in the combustion chamber is not rising adheres to the wall surface and is hard to evaporate. By decreasing the pilot injection amount as the pilot injection is earlier in the pilot injections of the times, it is possible to weaken the penetration force of the spray, and it is possible to reliably avoid the adhesion to the wall surface.

According to the invention of claim 5, when the rail pressure is excessively lowered, the spray is not atomized and the evaporation rate is lowered, but the amount of the first pilot injection is increased and the timing is advanced. Thus, the evaporation time and amount can be secured, and the oxidation reaction can be promoted before the main injection.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of a fuel injection device for a diesel engine showing an embodiment of the present invention. The fuel injection device of the diesel engine 1 is of a common rail type, and includes a supply pump 2 that supplies high-pressure fuel, a common rail 3 that accumulates high-pressure fuel from the supply pump 2, and a high pressure accumulated in the common rail 3. An injector 4 that directly injects fuel into the combustion chamber of each cylinder.

The injector 4 is, for example, Japanese Patent Laid-Open No.
As is well known from Japanese Patent Publication No. 153056, a needle valve is opened and closed by using a piezo element, and by controlling the piezo element with a signal from an engine control unit (hereinafter referred to as ECU) 10, The valve opening timing, valve opening time, and lift amount of the needle valve can be arbitrarily controlled.

Each detection signal is input to the ECU 10 from a rotation speed sensor 11 that detects an engine speed Ne, an accelerator opening sensor 12 that detects an accelerator opening Acc, and a water temperature sensor 13 that detects an engine cooling water temperature Tw. ing. In addition, when the common rail 3 is mounted,
A rail pressure sensor 14 is provided as an actual rail pressure detecting means for detecting an actual rail pressure Prail which is an actual fuel pressure in the inside, and a detection signal thereof is also input to the ECU 10.

Here, the ECU 10 sets the injection timings of the main injection and the pilot injection (valve opening timing of the needle valve) based on these signals, and also calculates each injection amount. In controlling the injection amount, the valve opening time of the needle valve is calculated according to the target injection amount and the actual rail pressure, and the operation command signal to the piezo element of the injector 4 is output at each injection timing in accordance with this. To do. At this time, the maximum lift amount of the needle valve can also be controlled.

Next, the flow of fuel injection control in this embodiment will be described with reference to the flow chart of FIG. Step 1
(Indicated as S1 in the figure. The same applies hereinafter), the engine speed Ne, the accelerator opening Acc, the cooling water temperature Tw, and the actual rail pressure Prail are read. In step 2, in accordance with the read engine speed Ne, accelerator opening Acc, cooling water temperature Tw, and actual rail pressure Prail, the main injection amount, pilot injection amount, main injection timing, pilot injection timing, and needle Set the maximum valve lift.

In step 3, based on the map of FIG.
From the engine speed Ne and the accelerator opening Acc, the target rail pressure Pm is set so that the higher the rotation speed and the higher the load, the higher the pressure becomes. This portion corresponds to the target rail pressure setting means. In step 4, it is judged whether or not the difference (Prail-Pm) between the actual rail pressure Prail and the target rail pressure Pm is larger than a predetermined value ΔP, and if it is larger, the routine proceeds to step 5.

In step 5, the pilot injection is divided into two times (first pilot injection and second pilot injection), and the first pilot injection timing and the second pilot injection timing are set respectively. Here, the first pilot injection timing is the engine speed N according to the map of FIG.
From e and accelerator opening Acc, set to advance (advance) at higher rotation speed and higher load side. Further, the second pilot injection timing is set to a timing that is as close as possible to the first pilot injection timing within the range of the responsiveness of the injector.

In step 6, the difference (Pra) between the actual rail pressure Prail and the target rail pressure Pm is calculated according to the table shown in FIG.
il−Pm), the first pilot injection amount and the second pilot injection amount are set respectively. That is, as the actual rail pressure Prail increases with respect to the target value Pm (Prail
The larger the value of −Pm), the larger the total injection amount of pilot injection, which is the sum of the first pilot injection amount and the second pilot injection amount, is set to be, but the first pilot injection amount is relatively small. It is set to a constant value, and the second pilot injection amount is set to increase as the actual rail pressure Prail rises with respect to the target rail pressure Pm. And
The main injection amount is the increase of the total injection amount of pilot injection,
Correct the weight loss.

In step 7, the difference (Pra) between the actual rail pressure Prail and the target rail pressure Pm is calculated according to the table shown in FIG.
il-Pm), set the maximum needle valve lift of the injector. That is, the actual rail pressure Prail is the target rail pressure P.
Correction is performed so that the needle valve maximum lift amount decreases as it increases with respect to m. FIG. 7 shows a schematic diagram of the fuel injection pattern (needle valve lift setting) set in steps 5 to 7.

Since the pilot injection is divided and the needle valve maximum lift amount is suppressed to be lower than in normal times (when the actual rail pressure is near the target rail pressure), the penetration force of the spray is weakened. Therefore, it is possible to suppress the adhesion of the spray to the wall surface. Further, among the divided pilot injections, the amount of the first pilot injection is made relatively small, so by further weakening the penetration force, even when the piston is rising and the temperature in the combustion chamber is not rising sufficiently The adhesion to the wall surface can be minimized and the deterioration of combustion can be avoided.

According to the judgment in the step 4, Prail-Pm
If ≦ ΔP, proceed to step 8. In step 8,
On the contrary, the difference between the target rail pressure Pm and the actual rail pressure Prail (P
m-Prail) is larger than a predetermined value ΔP,
If so, go to step 9.

In step 9, the pilot injection is divided into two times (first pilot injection and second pilot injection), and the first pilot injection timing and the second pilot injection timing are set respectively. Here, the first pilot injection timing is the engine speed N according to the map of FIG.
From e and accelerator opening Acc, set to advance (advance) at higher rotation speed and higher load side. The setting of the map of FIG. 8 is the same at the same engine speed and accelerator opening,
The setting is the same as or earlier than the setting of the map in FIG. The second pilot injection timing is set to a timing that is as close as possible to the first pilot injection timing within the range of the responsiveness of the injector.

In step 10, the difference (Pm) between the target rail pressure Pm and the actual rail pressure Prail is calculated according to the table shown in FIG.
-Prail), the first pilot injection amount and the second pilot injection amount are respectively set. That is, as the actual rail pressure Prail decreases with respect to the target value Pm (Pm-
As the Prail increases, the total injection amount of pilot injection, which is the sum of the first pilot injection amount and the second pilot injection amount, is set to increase, while the first pilot injection amount is set to be larger than the second pilot injection amount. Set to increase. Then, the main injection amount is reduced and corrected by the increase amount of the total injection amount of the pilot injection.

FIG. 10 shows a schematic diagram of the fuel injection pattern set in steps 9 to 10 described above. When the rail pressure is excessively reduced, the spray is not atomized and the evaporation rate is reduced, but the pilot injection is divided into two and the injection timing is advanced for the first pilot injection, and Since the injection amount is increased with respect to the second pilot injection, the evaporation time and the evaporation amount of the first pilot injection can be secured, and the oxidation reaction up to the main injection can be promoted. Can be stabilized.

In the judgment at the above step 8, Pm-Prail
If ≦ ΔP, that is, if the absolute value of the difference between the actual rail pressure Prail and the target rail pressure Pm is less than the predetermined value ΔP, the present flow is ended as it is, and the setting in step 2 is maintained to maintain the normal value. One pilot injection will be performed.
In the flow of FIG. 2, steps 5 and 9 serve as a means for dividing the pilot injection into a plurality of times when the absolute value of the difference between the actual rail pressure and the target rail pressure is equal to or greater than a predetermined value. Equivalent to.

Also, steps 6 and 10 (FIGS. 5 and 9)
Table) part increases the total injection amount in pilot injection and decreases the injection amount in main injection when the absolute value of the difference between the actual rail pressure and the target rail pressure exceeds a specified value. It corresponds to the means to do. Further, the step 7 corresponds to a means for reducing the maximum lift amount of the needle valve of the injector when the actual rail pressure exceeds the target rail pressure by a predetermined value or more.

In the step 6 (table in FIG. 5), when the actual rail pressure exceeds the target rail pressure by a predetermined value or more, the pilot injection with the earlier injection timing out of the plurality of pilot injections is It corresponds to a means for reducing the pilot injection amount. In addition, when the actual rail pressure is lower than the target rail pressure by a predetermined value or more, the portion of steps 9 and 10 (the map table of FIG. 8 and FIG. 9) is the first pilot injection of the plurality of pilot injections. With respect to, the injection timing is advanced and the injection amount is increased with respect to other pilot injections.

[Brief description of drawings]

FIG. 1 is a system diagram of a fuel injection device showing an embodiment of the present invention.

FIG. 2 is a flowchart of fuel injection control.

FIG. 3 is a diagram showing a map for setting a target rail pressure.

FIG. 4 is a diagram showing a map for setting a first pilot injection timing.

FIG. 5 is a diagram showing a pilot injection amount setting table.

FIG. 6 is a diagram showing a table for setting the maximum lift amount of the needle valve.

FIG. 7 is a schematic diagram showing an injection pattern when the rail pressure rises.

FIG. 8 is a diagram showing a map for setting a first pilot injection timing.

FIG. 9 is a diagram showing a pilot injection amount setting table.

FIG. 10 is a schematic diagram showing an injection pattern when the rail pressure drops.

FIG. 11 is a diagram showing a conventional behavior of rail pressure at the time of starting.

[Explanation of symbols]

1 diesel engine 2 supply pumps 3 common rail 4 injectors 10 ECU 11 Engine speed sensor 12 Accelerator position sensor 13 Water temperature sensor 14 Rail pressure sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 51/00 F02M 51/00 AF term (reference) 3G066 AA07 AB02 AC09 BA01 CC06U CE27 DA04 DA09 DB01 DB04 DC04 DC09 DC18 3G084 AA01 BA13 BA15 DA04 EA11 EB09 FA00 FA10 FA20 FA33 3G301 HA02 JA12 JA21 KA01 KA05 LB11 LC05 MA18 MA26 MA27 NA08 NC02 ND02 NE01 NE06 NE11 NE12 PB08A PE01Z PF03Z

Claims (5)

[Claims] 1. In a diesel engine equipped with a common rail fuel injection device, means for setting a target rail pressure, which is a target value of the fuel pressure in the common rail according to the engine operating state, and an actual value of the fuel pressure in the common rail. A means for detecting a certain actual rail pressure, and a means for dividing pilot injection performed prior to the main injection into a plurality of times when the absolute value of the difference between the actual rail pressure and the target rail pressure becomes a predetermined value or more, A control device for a diesel engine, comprising: 2. When the absolute value of the difference between the actual rail pressure and the target rail pressure exceeds a predetermined value, the total injection amount in pilot injection is increased and the injection amount in main injection is decreased. The diesel engine control device according to claim 1. 3. The actual rail pressure exceeds the target rail pressure by a predetermined value or more,
The control device for a diesel engine according to claim 1 or 2, wherein the maximum lift amount of the needle valve of the injector is reduced when it exceeds the limit. 4. The actual rail pressure is equal to or more than a predetermined value of the target rail pressure,
When it exceeds, among the pilot injections of a plurality of times, the pilot injection amount is reduced as the pilot injection is earlier, the pilot injection amount of the diesel engine according to any one of claims 1 to 3. Control device. 5. The actual rail pressure is greater than or equal to a target rail pressure by a predetermined value,
When it is below, the injection timing is advanced for the first pilot injection of the plurality of pilot injections, and the injection amount is increased with respect to other pilot injections. ~ The control device for a diesel engine according to claim 4.