JPH0295751A - Fuel injection controller for diesel engine - Google Patents

Abstract

PURPOSE:To bring out the effect of pilot injection to the largest possible extent as well as to make improvements in combustion efficiency of fuel by main injection by controlling the main injection's start timing so as to become a peak of fuel combustion by the pilot injection or the vicinity. CONSTITUTION:During engine driving, at a control unit 30, first of all, the injection quantity, injection rate and injection timing of fuel by pilot injection and the injection start timing of fuel by main injection are determined according to a driving condition. Then, is injection start timing by the main injection is controlled for alteration by a timer 25, while the fuel injection timing by the pilot injection is controlled by a solenoid valve 27. Next, a fuel combustion state by the pilot injection is detected from an output signal of a combustion sensor 37, and whether there is a combustion peak of pilot injection fuel or not is judged. When this judgment is NO, whether this combustion peak of the pilot injection fuel is more preceded than the start timing of the main injection or not is judged, and according to the judged result, timing delay or timing advance control over the constant specified value of pilot injection timing is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection control device for a day cell engine. The present invention relates to a fuel injection control device for a diesel engine that performs injection.

(Prior Art) Conventionally, as a fuel injection control device for this type of diesel engine, a plunger-type fuel injection control device is used for each cylinder of the engine, as disclosed in, for example, Japanese Patent Application Laid-open No. 165856/1983. It is known that a plurality of injection pumps are provided, one of which is used for pilot injection, and pilot injection of fuel is performed prior to main injection of fuel when the engine is under low load.

The purpose of such pilot injection is to shorten the ignition delay period of fuel caused by main injection and to reduce the initial combustion rate. The reason why such a purpose is achieved by pilot injection is thought to be due to the effect of increasing the temperature in the cylinder due to ignition of the viroft injected fuel, or the propagation of flame as a source of ignition.

In order to achieve the above purpose of pilot injection in a desirable manner, many studies have been conducted on the timing of main fuel injection and pilot injection. It has been proposed that correction control is performed based on factors such as , cooling water temperature, and transient conditions.

(Problems to be Solved by the Invention) However, there have been almost no studies or proposals regarding reliable and precise control, such as the relative relationship between main injection and pilot injection, or ignition detection feedback control based on this relative relationship. We will also discuss specific control methods to maximize the effects of pilot injection.
Almost no research or proposals have been made.

Therefore, the present invention controls the relative injection timing of main injection and biloft injection based on the correlation between main injection and pilot injection so as to maximize the effect of combustion of pilot injected fuel. The object of the present invention is to provide a fuel injection control device for a diesel engine that can perform the following steps.

(Background of the Invention) According to the sincere research conducted by the inventor of the present invention, when main injection of fuel is performed before or in the early stage of ignition of the pilot injected fuel, this main injection causes the flow and turbulence of the air-fuel mixture in the combustion chamber. In addition, the temperature inside the combustion chamber decreases due to the latent heat of vaporization. Therefore, in such an incomplete ignition state of the pilot-injected fuel, the main injection has a negative effect on the combustion of the pilot-injected fuel, resulting in extinguishing or half-burning. It became clear that the effect of pilot injection could not be obtained sufficiently. Therefore, it has been found that in order to achieve the above-mentioned object of the present invention, it is sufficient to reliably burn a small amount of fuel by pilot injection.

(Means for Solving the Problems) Therefore, the fuel injection control device for a diesel engine of the present invention includes a combustion peak detection means for detecting the peak of combustion of pilot-injected fuel or its vicinity, and a combustion peak detection means for detecting the combustion peak of pilot-injected fuel or the vicinity thereof, and , comprising a control means for controlling either or both of the main injection timing and the pilot injection timing so that the combustion peak of the fuel due to the pilot injection detected by the combustion peak detection means is at or near the peak. This is a characteristic feature.

(Effects of the Invention) As described above, in the diesel engine fuel injection control device of the present invention, the fuel injection by the main nozzle, that is, the start timing of the main injection is at or near the peak of fuel combustion by the pilot injection. As a result, the main injection is always performed after the pilot injection has ensured combustion of the fuel, maximizing the effect of the pilot injection and ensuring that the main injection is combusting the fuel in an appropriate manner. can.

(Embodiment) Hereinafter, a fuel M III control system for a diesel engine according to a preferred embodiment of the present station will be described with reference to the accompanying drawings. In the following embodiments, the diesel engine will be described as a four-cylinder engine.

FIG. 1 is an overall schematic configuration diagram of a diesel engine incorporating a fuel injection control device according to an embodiment of the present invention.
FIG. 2 is a side view including a partial cross section of the fuel injection pump of this diesel engine.

In these figures, reference numeral 1 indicates a day-cell engine, which has four cylinders 2.
2 is provided. A piston 3 is slidably fitted into each cylinder 2, and a combustion chamber 4 is formed within the cylinder 2 by the piston 3. An intake port 5 for supplying fresh air to each combustion chamber 4 and an exhaust boat 6 for discharging combustion gas from each combustion chamber 4 are also formed in the upper part of each cylinder 2. Further, an intake valve 7 for opening and closing the intake port 5 is provided at the opening of the intake port 5 to the combustion chamber 4, and a cough exhaust boat 6 is provided at the opening of the exhaust port 6 to the combustion chamber 4. Exhaust valves 8 for opening and closing are provided respectively.

Further, each cylinder 2 has a pilot nozzle 11 for injecting and supplying fuel into the combustion chamber 4, and a main nozzle 12.
are provided with their respective tips facing into the combustion chamber 4. The pilot nozzle 11 and the main nozzle 12 are each connected to a fuel injection pump 20 via a high pressure pipe 26.

As shown in FIG. 2, the fuel injection pump 20 is provided with a number of plungers 21, 21 corresponding to the number of pilot nozzles 11 and main nozzles 12.

A camshaft 22 driven by the engine 1 via a drive gear 1a is pivotally supported on the fuel injection pump 20, and the camshaft 22 includes a cam 23 for pilot injection of fuel and a cam 23 for main injection of fuel. 24 are provided.

In this configuration, the fuel injection pump 20 drives the plunger 2 of the corresponding pilot nozzle 11 by the pilot injection cam 23 to forcefully feed fuel to the pilot nozzle 11, and the main injection cam 2
4, the plunger 21 of the corresponding main nozzle 12
is driven to forcefully feed fuel to the main nozzle 12.

Each main injection cam 24 has a third cam lift characteristic.
The settings are as shown in the figure. In other words, this cam lift characteristic is a constant transmission type in which the cam lifts at a constant speed at the cam angle except at the beginning of lift and near the maximum lift. Further, the cam lift characteristics of each pilot injection cam 23 are set to an inconstant velocity type in which the lift speed gradually increases as the cam angle increases from the beginning of the lift, as shown in FIG. Therefore, by opening the pilot nozzle 11 at a cam angle at which the lift speed of the pilot injection cam 23 is small, the injection rate from the pilot nozzle 11 is changed to a small value independently from the main nozzle 12, and the lift speed is The injection rate changing device 40 is configured to greatly change the injection rate of l fuel by opening the pilot nozzle 11 at a cam angle of 1.

Moreover, as shown in FIG. 2, each pilot nozzle 11
A high-speed electromagnetic valve 27 is provided in each of the high-pressure pipes 26, and fuel can be supplied to the pilot nozzle 11 only when the electromagnetic valve 27 is open. That is, the injection timing changing device 4 is configured to change the injection timing of fuel from the pilot nozzle 11 independently from the main nozzle 12 by operating the electromagnetic valve 27 during that time.
1.

A timer 25 is interposed between the camshaft 22 and its drive gear 1a to adjust the fuel injection timing by changing the relative position of the two in the rotational direction. Although not shown, the main injection plunger 21 is provided with a control lever that operates depending on the operating state of the engine. injection plunge,
The amount of fuel injection from -21 is mechanically adjusted.

The operation of the fuel injection pump 20 is controlled by a control unit 30 composed of, for example, a microcomputer. The control unit 30 is provided with a pilot nozzle 11,
A pilot needle valve lift sensor 31 that detects the lift of the needle valve of the nozzle, and a main needle valve lift sensor 32 that is provided in the main nozzle 12 and detects the lift of the needle valve of the nozzle.
, a rotation speed sensor 33 as a rotation speed detection means for detecting the rotation speed of the engine 1; an accelerator opening sensor 34 as a load detection means for detecting the load on the engine 1 based on the accelerator opening; ,
A water temperature sensor 35 that detects the cooling water temperature, a crank angle sensor 36 that detects the top dead center position of each piston 3, and a combustion chamber 4
a combustion sensor 37 that detects the combustion state of fuel in the intake passage; an intake sensor 38 that is installed in the intake passage and detects the intake air temperature;
and an atmospheric pressure sensor 39 that detects atmospheric pressure are connected respectively. As the combustion sensor 37, a type that detects the temperature within the combustion chamber 4, a type that detects the color of the flame within the combustion chamber 4, a type that detects the pressure within the combustion chamber 4, etc. are used. be able to. The control unit 30 receives output signals from these sensors 31 to 39, controls each plunger 21, type 25, and solenoid valve 27 according to these output signals, and operates according to the operating condition of the engine 1. Accordingly, the injection type, injection rate, and injection timing of each fuel are adjusted and controlled in pilot injection and main injection of fuel.

Next, the control of the pyro injection (7) and main injection of fuel by the control unit 30 will be explained with reference to the flowchart of FIG. 5.

This control first includes the viroft needle valve lift timing (pilot injection timing), main needle valve lift timing (main injection timing), engine speed, and
Reading of detection signals related to engine load, engine cooling water temperature, piston top dead center position, fuel combustion state, intake air temperature, and atmospheric pressure (intake pressure), and fuel amount adjustment provided near the main injection plunger 21 The process starts by reading a detection signal related to the opening degree of the control lever (step Sl). Next, in step S2, the operating conditions of the engine I are determined based on the read detection signal.

After that, in step S3, the fuel injection amount, injection rate, and injection timing (injection start timing and injection end timing) for pilot injection and the injection timing for main injection are determined according to the engine operating conditions determined as above. The fuel injection start timing is determined. The fuel injection start timing for main injection is determined based on the current engine rotational speed and the injection start timing map for main injection, which is preset according to the engine rotational speed and engine load, so that the fuel ignition timing is appropriate. and engine load.

Next, in step S4, the injection start timing of the main injection is changed and controlled by the timer 25 so that the injection start timing, injection type, and injection rate are each set to the set values, and the timer 25 of the pyro/) injection is changed. Pyro corresponding to the above setting injection rate! ) When the injection cam 23 is lifted 1, the solenoid valve 27 is operated and controlled so that the fuel injection timing (start and end) is set to the set value.

After that, in step S5, based on the output signal from the combustion sensor 37, the ignition state of the fuel due to the pilot injection, that is, the combustion state is detected.

At this time, a sensor that detects the combustion pressure waveform in the combustion chamber 4 is used as the combustion sensor 37, and the pressure waveform is converted into a heat release rate to detect the combustion state in the combustion chamber 4. The heat generation patterns within can be roughly divided into those shown by Ll, L2, and L3 in FIGS. 6 to 8. That is, when the injection timing of pilot injection and main injection is appropriate, as shown in FIG. 6, complete ignition of the pilot injected fuel, that is, combustion peak P1 can be confirmed, and as shown in FIG.
The conditions become worse as shown in Figure 8, and in the heat generation pattern, that is, the combustion pattern, shown in Figure 7, due to the slight combustion peak P2, incomplete pyrolysis and ignition of the throat-injected fuel occur. However, the heat generation pattern shown in Figure 8 makes it impossible to detect the combustion peak.As mentioned above, as shown in Figure 6, the pilot injected fuel is completely In case 1, that is, when combustion peak P1 exists, the ignition delay of the main injected fuel becomes small, initial combustion can be suppressed, and desirable ignition 99 is achieved.

Therefore, in this embodiment, the following control is performed after this. First, in step S6, it is determined whether a combustion peak of pilot injected fuel exists. If this determination is YES, the combustion peak position of the pyro-nod injected fuel is detected in step S7, and then in step S8
Detects the start time of main injection. Following these detections, in step S9, it is determined whether the combustion peak of the pilot injected fuel coincides with the start timing of main injection or is close to it.

When this determination is NO, the following control is performed in order to match the combustion peak of the pilot injected fuel with the start timing of main injection. That is, in step S10, it is determined whether the combustion peak of the pilot injected fuel is before the start time of main injection, and when this determination is YES, retard control is performed during a constant predetermined period of the pilot injection time (step S10).
l), On the other hand, if this determination is No, step S1
In step 2, the pilot injection timing is advanced by a certain amount, and then the process returns to the start.

On the other hand, when the determination in step S6 is No, that is, when there is no combustion peak of the pilot injected fuel, advance control of the pilot injection timing is performed by a certain predetermined amount in step S13, and when the determination in step S9 is YES, the pilot injection timing is advanced by a certain amount. That is, when the combustion peak of the pilot injected fuel matches or is close to the start timing of main injection, the control returns to the start in the same way.

As described above, according to the embodiments described above, the combustion peak of the pilot injected fuel can be made to coincide with or be located near the start timing of the main injection, thereby allowing the main injection fuel to be combusted in a desired state. Furthermore, if the pyro 7) injection of fuel continues even after the complete ignition of the pyro 7) injected fuel, the premixed fuel proportion of the main injected fuel is increased, and the main injected fuel is This increases the combustion peak of the main injected fuel, that is, increases the combustion temperature, increases the generation of nitrogen oxides, and the pyloft injection actually makes the combustion state of the main injected fuel undesirable. Therefore, it is desirable to cut the pilot-injected fuel after the pilot-injected fuel is completely ignited. In the above embodiment, the combustion peak of the pilot injected fuel was detected and the injection timing was controlled so as to match the start timing of main injection with this combustion peak. As described above, the start of combustion after the combustion peak PIO of the pilot injected fuel may be detected, that is, determined to be the combustion timing of the main injection, and based on this detection, the timing of the pilot injection, its amount, etc. may be controlled. .

Further, in the above embodiment, only the pilot injection timing is controlled, but the main injection timing, or both the main injection timing and the pilot injection timing may be controlled.

Furthermore, in the above embodiment, dedicated nozzles are used for pilot injection and main injection, but the fuel injection pump may be configured to have one injection nozzle and perform pilot injection and main injection.

[Brief explanation of drawings]

FIG. 1 is an overall schematic configuration diagram of a day cell engine incorporating a fuel injection control device according to an embodiment of the present invention; FIG. 2 is a side view including a partial cross section of the fuel injection pump of the diesel engine; Figure 3 is a characteristic diagram of the cam for main injection, Figure 4 is a characteristic diagram of the cam for pilot injection, Figure 15 is a flowchart diagram showing fuel injection control from the pilot nozzle and the main nozzle by the control unit. FIG. 6, FIG. 7, and FIG. 8 are diagrams showing differences in the combustion state in the combustion chamber due to the difference in injection timing between pilot injection and main injection with respect to the t-th objective, respectively. 1 day cell engine, 4 combustion chamber, 11
Pilot nozzle, 12 Main nozzle, 20 Fuel injection pump, 23 Pilot injection cam, 27
High speed solenoid valve, 30 control unit), 37
Combustion sensor, 41 injection timing change device.

Claims (1)

[Claims] A main injection that injects most of the supplied fuel in one stroke into the combustion chamber, and prior to the main injection,
A fuel injection control device for a diesel engine configured to perform a pilot injection in which a small amount of supplied fuel is injected, comprising a combustion peak detection means for detecting a combustion peak or the vicinity thereof of the pilot injected fuel, and a start of the main injection. control means for controlling either or both of the main injection timing and the pilot injection timing so that the timing is at or near the peak of fuel combustion due to the pilot injection detected by the combustion peak detection means. Diesel engine fuel injection control device.