JP2846969B2 - Fuel injection control device for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a diesel engine, and more particularly to an unburned H during a low to medium load operation.
The present invention relates to a device that reduces C and reduces smoke during high-load operation.

[0002]

2. Description of the Related Art Particulates (fine particles) contained in exhaust gas of a diesel engine are mainly composed of soluble organic components (unburned HC) and smoke, and reduction of these unburned HC and smoke is particularly demanded. However, effective measures have not yet been established.

[0005] As shown in FIG. 15, when the load is low and medium, the combustion chamber gas temperature is low, and the amount of unburned HC is large. However, the amount of smoke is small because the fuel injection amount is small and the air amount is excessive. On the other hand, at high load, the combustion chamber gas temperature is high, so the emission amount of unburned HC decreases, but the fuel injection amount increases, and the mixing between fuel and air becomes insufficient. Smoke emission increases due to reasons such as a longer combustion speed. Therefore, it is effective to suppress the generation of unburned HC at low and medium loads and to suppress the generation of smoke at high loads.

[0004] Incidentally, in order to suppress the generation of unburned HC, it is desirable to lower the injection pressure to shorten the reach of the injected fuel. On the other hand, in order to suppress the generation of smoke, it is desirable to promote mixing of the spray of the injected fuel with air and to promote oxidation of carbon particles by high-speed combustion. There are a fuel injection quantity, an injection period, and an injection pressure as physical quantities of the injected fuel, and one of these two physical quantities determines the remaining one physical quantity.

Recently, in order to improve the fuel injection control, a high-pressure fuel pump, an accumulator for accumulating pressurized fuel, and a pressurized fuel for the accumulator are provided in a fuel supply system as disclosed in Japanese Patent Application Laid-Open No. 2-37152. An operation in which a unit injector with an electromagnetic switching valve that injects fuel upon receipt of the pressure and an electromagnetic relief valve that adjusts the fuel pressure in the accumulator, that is, the injection pressure, is provided and the injection pressure is determined by the engine speed and the accelerator opening or the engine load There is known one that changes according to the state.

[0006]

In the prior art, such as the unit injector type fuel injection control device disclosed in the above-mentioned publication, the injection pressure is determined in accordance with the operating state determined by the engine speed and the accelerator opening, and this injection pressure and the necessary A control that determines the injection period based on the appropriate fuel injection amount has been adopted. By the way, in order to suppress the generation of smoke as described above, it is necessary to (A) promote mixing of spray and air and (B) promote oxidation of carbon particles by high-speed combustion within a short time. Although it is desirable, if the injection period is lengthened to promote mixing, the degree of high-speed combustion is reduced, which is disadvantageous in promoting oxidation of carbon particles. That is, in order to reduce the smoke at the time of high load, it is necessary to set an optimal injection period that is neither too long nor too short from the viewpoint of the above (A) and (B). Since the injection amount and injection pressure are determined prior to the injection period,
It has been difficult to set the injection period to an optimal period.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel injection control device for a diesel engine capable of reducing the amount of smoke generated at a high load, and to reduce the amount of unburned HC generated at a low load. An object of the present invention is to provide a fuel injection control device for a diesel engine.

[0008]

According to a first aspect of the present invention, there is provided a fuel injection control apparatus for a diesel engine, as shown in a functional block diagram of FIG. An operation state detection for detecting an operation state of a diesel engine in a diesel engine fuel injection control device including an injector and pressure regulating means for adjusting an injection pressure of injected fuel, and controlling an injection pressure, an injection period, and an injection timing. Means, an injection amount setting means for setting a fuel injection amount corresponding to the detected operating state,
Control means for setting the injection period to a substantially constant period so that the amount of smoke generated during high-load operation is minimized and setting the injection pressure based on the injection period and the fuel injection amount. .

According to a second aspect of the present invention, there is provided a fuel injection control apparatus for a diesel engine according to the first aspect, wherein the control means reduces the injection pressure during a high load operation during a low and medium load operation. The injection pressure is controlled to be higher than the injection pressure.

According to a third aspect of the present invention, in the fuel injection control apparatus for a diesel engine according to the second aspect, the control means includes: a load detected during low-medium load operation; It is configured to set the injection pressure based on predetermined characteristics that are set in advance so as to increase the injection pressure in accordance with the increase, and to set the injection period based on the injection pressure and the fuel injection amount. Things.

[0011]

In the fuel injection control device for a diesel engine according to the first aspect, the operating state detecting means detects the operating state (speed and load) of the diesel engine, and the operating state detected by the injection amount setting means. When the fuel injection amount corresponding to the fuel injection amount is set, the control means sets the injection period to a substantially constant period so that the amount of smoke generation becomes as small as possible during high load operation, and based on the injection period and the fuel injection amount. To set the injection pressure. As described above, since the injection period at the time of high load operation is set to a substantially constant period so that the amount of smoke generation becomes as small as possible, the amount of smoke generation at the time of high load operation can be reduced.

In the fuel injection control device for a diesel engine according to the second aspect, basically the same operation as that of the first aspect is obtained. In addition, since the control means sets the injection pressure at the time of high load operation higher than the injection pressure at the time of low and medium load operation, the mixing of the spray and air is promoted by the finer spray of the injected fuel during the high load operation; The high kinetic energy imparted to the spray promotes the mixing of the spray and the air, thereby further reducing the amount of smoke generated during high load operation.

According to the fuel injection control device for a diesel engine according to the third aspect, basically the same operation as that of the second aspect is obtained. In addition, the control means adjusts the injection pressure based on a predetermined characteristic that is set in advance so that the injection pressure increases in accordance with the increase in the load during low-medium load operation, and the load detected by the operation state detection means. In addition to the setting, since the injection period is set based on the injection pressure and the fuel injection amount, the reach of the injected fuel that is injected at a low injection pressure corresponding to the load becomes short, and during low to medium load operation. The amount of unburned HC generated is reduced.

[0014]

According to the fuel injection control device for a diesel engine according to the first aspect, the operation state detecting means, the injection amount setting means, and the control means are provided. In addition, the amount of smoke generated during high-load operation can be reduced.

According to the fuel injection control device for a diesel engine according to the second aspect, basically the same effects as those of the first aspect can be obtained as described in the above-mentioned operation. In addition, by setting the injection pressure during high load operation higher than the injection pressure during low and medium load operation, the amount of smoke generated during high load operation can be further reduced.

According to the fuel injection control device for a diesel engine according to the third aspect, basically the same effects as those of the second aspect can be obtained as described in the section of the operation. In addition, the amount of unburned HC generated during low-medium load operation can be reduced.

[0017]

FIG. 1 to FIG. 14 show an embodiment of the present invention.
This will be described with reference to FIG. The present embodiment is an example in which the present invention is applied to a fuel injection system of a four-cylinder in-line diesel engine for an automobile. The overall configuration of the fuel injection system will be described with reference to FIG. A fuel injection system of a diesel engine 1 (hereinafter referred to as an engine) includes a high-pressure fuel pump 2 driven by the engine 1 and an accumulator 3 for accumulating fuel pressurized by the fuel pump 2.
And an electromagnetic three-way relief valve 5 provided in a fuel passage 4 leading from the fuel pump 2 to the accumulator 3, and four pressurized fuels connected to the accumulator 3 via the fuel supply passage 6 and supplied from the accumulator 3, respectively. Four sets of unit injectors 7 for supplying fuel to the combustion chambers of the cylinders,
A drive circuit unit 8 that supplies drive pulses to the electromagnetic switching valves of the set of unit injectors 7, a control unit 10, and sensors are provided. Reference numeral 9 denotes a fuel tank.

The sensors include a fuel pressure sensor 11 for detecting the fuel pressure in the accumulator 3, a well-known crank angle sensor 12 for detecting the rotation angle of the crank angle by an electromagnetic pickup sensor, and a reference timing of a reference cylinder (for example, , Intake TDC) and a well-known reference crank angle sensor 13 and an accelerator opening provided in association with an accelerator pedal and corresponding to an accelerator depression amount (this corresponds to an engine load) are detected by a potentiometer or the like. An accelerator opening sensor 14, a water temperature sensor 15 for detecting the temperature of the engine cooling water, an air temperature sensor 16 for detecting the temperature of the air taken in upstream of the intake passage, and a pressure sensor 17 for detecting the air pressure. The detection signals of these sensors 11 to 17 are supplied to the control unit 10 respectively. That. The control unit 10
A control signal is output to the drive circuit unit 8 to control the four unit injectors 7, and a drive pulse is output to the solenoid of the electromagnetic three-way relief valve 5 to control the fuel pressure in the accumulator 3, that is, the injection pressure. .

The structure of the unit injector 7 will be briefly described with reference to FIG. Unit injector 7
Consists of an injector body 20 and an electromagnetic switching valve 21 attached to the upper end thereof. In the injector body 20, a needle valve 23 is formed at the lower end of a needle valve body 22, and the needle valve body 22 is The first spring 25 urges the valve 27 toward the valve closing side.
The lower end of the rod 27 a of the piston 27 urged downward by the second spring 28 abuts the spring receiver 24, and the orifice 30 of the spring receiver 29 is connected to the control pressure port of the electromagnetic switching valve 21. 31. Needle valve 2
An outlet chamber 32 is formed on the outer peripheral side of the lower half of the fuel tank 2, and pressurized fuel is supplied from the accumulator 3 to the outlet chamber 32 via the fuel supply passage 6. The needle valve 22 receives the fuel pressure in the outlet chamber 32. Is urged upward.

In the electromagnetic switching valve 21, the control pressure port 3
The first valve body 34 is housed in the valve hole 33 on the upper side of the first valve body 34, and the first valve body 34 is configured to open and close between the control pressure port 31 and the drain passage 35. Is connected to the control pressure port 31 through a center hole 37, a second valve body 38 is slidably mounted at the center of the upper end of the first valve body 34, and a center hole is formed at the lower end of the second valve body 38. 37 is configured to be openable and closable, the second valve body 38 is urged downward by a valve closing spring 39, and the first valve body 3 is energized when a solenoid 48 is energized.
Numeral 4 raises and opens the valve against the valve-closing spring 39 to connect the control pressure port 31 to the drain passage 35, and at the same time, the second valve body 38 closes the center hole 37. An input port 41 is formed outside the middle portion of the first valve body 34, and the input port 41 is connected to the fuel supply path 6 via an input path 42,
As shown, when the solenoid 40 is turned off and the first valve body 34 is in the closed position, the input port 41 and the inner chamber 36 are communicated with each other through the input hole 43 of the first valve body 34.

Therefore, when the solenoid 40 is OFF, the first valve body 34 is in the closed position and the control pressure port 31 and the drain passage 35 are shut off. 42, input port 41, input hole 43, inner chamber 36, center hole 37, control pressure port 31, orifice 3
0, the pressure receiving chamber 26a is filled, and the piston 27 is strongly urged downward, so that the needle valve body 22 pushed by the piston 27 is at the lower limit position and the injection port 44 is closed by the needle valve 23. Is not injected. On the other hand, when the solenoid 40 is energized, the first valve body 34 rises and moves to the open position, and the second valve body 38 descends relatively to the first valve body 34 to move the center hole 37. Is closed, the fuel pressure in the pressure receiving chamber 26a decreases to the drain pressure, and the needle valve 22 rises due to the fuel pressure in the outlet chamber 32, and fuel is injected from the injection port 44.

The control unit 10 includes an A / D converter for A / D converting detection signals from the sensors 11 and 14 to 17.
A converter, a circuit for shaping the waveforms of the detection signals from the sensors 12 and 13, an input / output interface, a CPU, a ROM and an R
A microcomputer having an AM and a drive circuit for the electromagnetic three-way relief valve 5 are provided. The ROM has a control program for fuel injection control to be described later and various maps (or tables, calculations, A control program for fuel injection execution control for sequentially driving the four unit injectors 7 in response to the data of the injection timing and the injection period determined by the fuel injection control is input and stored in advance. However, the fuel injection execution control is based on the pulse signal obtained from the crank angle sensor 12, the pulse signal of the reference crank angle from the reference crank angle sensor 13, the clock pulse signal, and the like. It is a well-known general control that constantly monitors whether or not the injection has been performed and causes the corresponding unit injector 7 to execute the injection during the injection period every time the injection timing comes, so that the detailed description thereof will be omitted.

Next, the fuel injection control for determining the injection pressure, the injection period, and the injection timing will be described. First,
Referring to FIGS. 3 to 6, as shown in FIGS. 3 and 4, when the load is low and medium, the soluble organic component (unburned H
Since the amount of C) increases as the injection pressure increases, it is desirable to use the lowest possible injection pressure in order to reduce the amount of unburned HC generated. Has little to do with the size of Therefore, in the low-medium load operation state, the injection pressure is set to be low and increases according to the increase in the load, and the fuel injection amount and the injection pressure determined from the map according to the detected operation state are determined. The injection period is set based on this.

As shown in FIGS. 5 and 6, when the load is high, the amount of generated smoke decreases as the injection pressure increases. Therefore, to reduce the amount of generated smoke, the injection pressure must be increased. It is desirable to set the injection period to an appropriate range in order to minimize the amount of smoke generated. Therefore, in the high load operation state, the injection period is set to a substantially constant period (for example, a value near Tem in FIG. 6) in which the amount of smoke generation is as small as possible, and is determined from the map according to the detected operation state. The injection pressure is set based on the fuel injection amount and the injection period set as described above. However, it is assumed that the injection pressure is set higher than in the low-medium load state.

Next, a map which is stored in the ROM in advance along with the control program for the fuel injection control will be briefly described. The control zone map shown in FIG. 7 includes an injection pressure control zone (corresponding to a low-to-medium load operation region) in which the injection pressure is set prior to the injection period, and an injection period prior to the injection pressure which is optimized as much as possible. FIG. 3 shows an injection period control zone to be set (corresponding to a high-load operation region). The map of the fuel injection amount Q in FIG. 8 shows an example in which the fuel injection amount Q (the injection amount per injection of each injector) is set for the entire operation region using the engine speed and the accelerator opening as parameters. Things.

The map of the injection pressure shown in FIG. 9 shows an example in which the injection pressure is set in the low-to-medium load region. In the high-load operation, the relationship is set by calculation based on the fuel injection amount and the injection period. Above, the injection pressure in the high load region in FIG. 9 is shown by the approximate injection pressure set by the above calculation for reference. FIG. 10 shows the injection pressure at a certain engine speed in the map of FIG. The map of the injection period in FIG. 11 shows an example of the injection period in a high-load region by a crank angle (deg), and the time per 1 degree of the crank angle decreases as the engine speed increases. In consideration of this, it is set larger on the higher rotation side. However, this injection period corresponds to Tem in FIG. 6 and is set to an optimal value so that the amount of smoke generated under a high load is minimized. FIG. 12 is a map of the injection period supplementing the map of FIG. 11, and shows an example of the injection period when the rotation speed is 50% of the maximum rotation speed, and is substantially constant in the high load region. Is set to The injection period in the low-to-medium load region shows an approximate injection period set by calculation based on the fuel injection amount and the injection pressure for reference. The injection timing map of FIG. 13 indicates that the injection timing (injection start timing) for the entire operation region is determined by the crank angle (de) before compression TDC.
g) shows an example.

Next, a fuel injection control routine performed by the control unit using the above-described maps will be described with reference to a flowchart of FIG. In the drawing, Si (i = 1, 2,...) Indicates each step. When the control is started at the same time as the start of the engine, necessary initial settings are executed in a memory such as a RAM (S1), and then various detection signals are read from the sensors 11 to 17 (S2). The engine speed is calculated based on the angle signal (S3), and the current operating state determined by the engine speed and the detected accelerator opening is determined by the injection pressure control zone (that is, the injection pressure control zone in the control zone map of FIG. 7). (S4). However, it is also possible to omit the map of FIG. 7 and make the determination based on the accelerator opening. Next, in S4, Ye
When it is determined to be s, the fuel injection amount Q corresponding to the current operation state is calculated using the map of FIG. 8 (S5).
However, temperature correction and density correction are performed on the fuel injection amount Q using the air temperature and the atmospheric pressure detected by the sensors 16 and 17.

Next, the injection pressure corresponding to the current operation state is calculated using the map of FIG. 9 (S6), and is then expressed by the formula of fuel injection quantity Q = constant × injection period × injection pressure. From the above, the injection period is calculated by applying the obtained fuel injection amount and injection pressure to the above formula (S7), and then the injection timing corresponding to the current operation state is calculated using the map of FIG. (S8) Next, in S9, a drive pulse corresponding to the injection pressure is output to the solenoid of the electromagnetic three-way relief valve 5 via the drive circuit, and the accumulator 3
Is adjusted to the injection pressure, and the data of the injection timing and the injection period are output to the fuel injection execution control. Thereafter, the process returns from S9 to S2, and the process from S2 is repeated every predetermined minute time.

In the fuel injection execution control, a drive current is supplied to the solenoid 40 of the injector 7 corresponding to the cylinder through the drive circuit unit 8 only during the injection period every time the injection timing of each cylinder is reached. Execute fuel injection.

When the current operation state enters the high load region, that is, the injection period control zone, it is determined as No in S4, and S10
Then, in S10, the fuel injection amount Q is calculated in the same manner as in S5, and then the injection period corresponding to the current rotational speed is set in FIG.
1 and the map of FIG. 12 (S11), then the injection pressure is calculated using the fuel injection amount Q, the injection period and the above formula (S12), and then the injection timing in S13 as in S8. Is calculated, the process proceeds from S13 to S9.

Next, the operation of the fuel injection control described above will be described. In the low-medium load operation state, the injection pressure is set higher than the injection period so that the injection pressure becomes lower as a whole and increases as the load increases. Since the combustion temperature is prevented from lowering due to the combustion in the narrow area and the amount adhering to the wall surface of the cylinder or piston is reduced, the unburned H
The generation amount of C is remarkably reduced. Further, since the fuel injection amount Q is small and the mixing of the spray and the air is sufficient in the excess air state, the amount of smoke generated is small. Note that even if the injection period becomes shorter, the amount of unburned HC generated is hardly affected.

At the time of high load operation, the amount of unburned HC generated is relatively small because the combustion temperature in the combustion chamber is sufficiently high. On the other hand, since the injection period is set to an optimum substantially constant period so as to minimize the amount of smoke generated as much as possible over the injection pressure, the amount of smoke generated can be significantly reduced. In addition, since the injection pressure is set higher than in the low-medium load operation state, the atomization of the spray is promoted, and high kinetic energy is applied to the individual particles of the spray, so that the mixing of the spray and the air is promoted. As a result, the amount of smoke generated is further reduced.

It should be noted that it is also possible to previously set a map of the injection period based on the map of the fuel injection amount and the map of the injection pressure in the low-medium load region. In this case, step S5 is omitted. It is possible to On the other hand, it is also possible to set a map of the injection pressure in advance for the high load region based on the map of the fuel injection amount and the map of the injection period, and in this case, the step of S10 can be omitted. It is. In the above embodiment, the case where the accumulator-type unit injector using the accumulator 3 is provided is described. However, instead of this, a pressure-intensifying unit injector (an electrically controlled injector is provided, and a plunger-type fuel pump and The present invention can be similarly applied to a device provided with a pressure adjusting means.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel injection system for a diesel engine according to an embodiment.

FIG. 2 is a cross-sectional view of the unit injector of FIG.

FIG. 3 is a diagram showing characteristics of a soluble organic component with respect to injection pressure.

FIG. 4 is a diagram showing characteristics of a soluble organic component with respect to an injection period.

FIG. 5 is a diagram showing characteristics of smoke with respect to injection pressure.

FIG. 6 is a diagram showing characteristics of a smoke injection period.

FIG. 7 is an explanatory diagram of a control zone map.

FIG. 8 is a diagram showing a fuel injection amount map.

FIG. 9 is a diagram showing an injection pressure map.

FIG. 10 is an explanatory diagram of the injection pressure map of FIG. 9 when the engine speed is constant.

FIG. 11 is a diagram of an injection period map.

12 is an explanatory diagram when the engine speed is constant in the injection period map of FIG. 11;

FIG. 13 is a diagram showing an injection timing map.

FIG. 14 is a flowchart of a fuel injection control routine.

FIG. 15 is a functional block diagram showing the configuration of the present invention.

FIG. 16 is an explanatory diagram relating to particulates contained in exhaust gas of a diesel engine according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 High-pressure fuel pump 3 Accumulator 5 Electromagnetic three-way relief valve 7 Unit injector 8 Drive circuit unit 10 Control unit 12 Crank angle sensor 14 Accelerator opening sensor 21 Electromagnetic switching valve

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (3)

(57) [Claims] 1. An injection control device comprising: a high-pressure fuel pump; an electrically controlled injector for injecting fuel into a combustion chamber; and pressure regulating means for adjusting the injection pressure of the injected fuel; and controls the injection pressure, the injection period, and the injection timing. In a fuel injection control device for a diesel engine, an operation state detection unit that detects an operation state of the diesel engine, an injection amount setting unit that sets a fuel injection amount corresponding to the detected operation state, and an injection period during high-load operation. A fuel injection system for a diesel engine, comprising: control means for setting a substantially constant period so as to minimize the amount of smoke generated and setting an injection pressure based on the injection period and the fuel injection amount. Control device. 2. The diesel engine according to claim 1, wherein said control means controls the injection pressure at the time of high load operation to be higher than the injection pressure at the time of low and medium load operation. Fuel injection control device. 3. The control means sets the injection pressure based on the detected load and a predetermined characteristic set so as to increase the injection pressure in accordance with the increase in the load during low to medium load operation. The fuel injection control device for a diesel engine according to claim 2, wherein the injection period is set based on the injection pressure and the fuel injection amount.