JP2002357154A - Fuel injection device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a combustion noise by improving combustibility of a diesel engine. SOLUTION: In this device, when a change rate of pressure in a cylinder is high by dividing main injection (a) and making a valve lift amount variably controllable of a fuel injection valve (c), and by decreasing a lift amount in the beginning and so on, an injection rate in the beginning is decreased, and by concurrently using delay angle control in addition to these factors [(b), (c)], the change rate of pressure in a cylinder is reduced, and a combustion noise is reduced.

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 a technique for improving combustion characteristics by controlling an injection rate in accordance with a change in cylinder pressure.

[0002]

2. Description of the Related Art As a fuel injection control device for a diesel engine, for example, a technology disclosed in Japanese Patent Application Laid-Open No. 11-173201 is known. In this conventional technique, the heat generation rate of pilot injection is obtained from the in-cylinder pressure, and the pilot injection timing and injection amount are controlled.

[0003]

However, in the control of the pilot injection as in the above-mentioned prior art, there is a limit in suppressing rapid combustion. The present invention has been made in view of such a conventional problem, and unlike pilot injection, the injection rate is controlled variably from the start of fuel injection to the end thereof, so that rapid injection is achieved. It is an object of the present invention to provide a fuel injection control device for a diesel engine capable of suppressing combustion and realizing a gradual change in combustion pressure, thereby effectively reducing combustion noise.

[0004]

For this purpose, the invention according to claim 1 comprises a fuel injection means for directly injecting fuel into a combustion chamber of an engine, an in-cylinder pressure detection means for detecting an in-cylinder pressure of the engine, An in-cylinder pressure change rate calculating means for calculating an in-cylinder pressure change rate based on the in-cylinder pressure detection value; and Injection rate control means for making the initial stage smaller than the latter period.

According to the first aspect of the invention, by controlling the fuel injection rate in accordance with the in-cylinder pressure change rate, it is possible to suppress a sudden increase in the in-cylinder pressure at the start of combustion. And combustion noise can be reduced. The invention according to claim 2 is characterized in that the injection rate control means delays the fuel injection timing as the in-cylinder pressure change rate increases.

According to the second aspect of the invention, the combustion noise can be further reduced by delaying the fuel injection timing in addition to reducing the initial injection rate during the fuel injection period. That is, although the in-cylinder pressure after the start of combustion also increases with an increase in the injection rate in the middle period during the fuel injection period, the fuel injection period is retarded according to the in-cylinder pressure change rate, so that the fuel injection The timing at which the injection rate in the middle of the period increases is set to a timing far from the compression top dead center, whereby it is possible to suppress a sudden increase in the in-cylinder pressure after the start of combustion, so that combustion noise can be further reduced.

According to a third aspect of the present invention, the injection rate control means injects fuel by dividing the fuel at a larger number of times during the fuel injection period as the in-cylinder pressure change rate increases. In each of the injection times, the injection amount of the subsequent injection is increased. According to the invention according to claim 3, as the in-cylinder pressure change rate is larger, the injection rate is averagely reduced by increasing the number of divisions in the divided injection,
In addition, by increasing the injection amount in the later injection, the injection rate characteristics in which the initial injection rate is further reduced are obtained, and an operation with small combustion fluctuation can be performed.

According to a fourth aspect of the present invention, the fuel injection means includes a needle valve for injecting fuel by a lift, and a solenoid for lifting the needle valve while a command voltage is applied. Wherein the injection rate control means controls the number of injections by the number of times the command voltage is applied during the fuel injection period, and injects the command voltage divided into a plurality of times at each application time of the command voltage. It is characterized by controlling time.

According to the fourth aspect of the present invention, when a fuel injection valve that lifts the needle valve on and off with a solenoid is used, the number of divisions and the injection time for each injection are controlled by the number of times the command voltage is applied. By doing so, the initial injection rate can be reduced in a pseudo manner. In the invention according to claim 5, the fuel injection means increases a lift amount of the needle valve by injecting fuel at a higher injection rate as the lift amount increases, and increases the lift amount of the needle valve as the applied command voltage increases. It is characterized by comprising a fuel injection valve having a piezoelectric element.

According to the fifth aspect of the present invention, the injection rate can be arbitrarily controlled according to the lift amount by using the fuel injection valve that controls the lift amount of the needle valve by the piezoelectric element. The invention according to claim 6 is characterized in that the injection rate control means reduces the initial value of the injection rate when the rate of change of the in-cylinder pressure exceeds a predetermined value, as compared with the latter rate during the fuel injection period. Features.

According to the sixth aspect of the invention, when the in-cylinder pressure change rate is large, the initial injection rate is made small so that the injection rate characteristic is reduced, so that the in-cylinder pressure change rate is reduced and the combustion fluctuation is small. It can be performed. In the invention according to claim 7, the fuel injection pressure can be adjusted by adjusting the fuel pressure in the common rail, and the injection rate control means performs the control of the injection rate together with the adjustment of the fuel injection pressure. It is characterized by.

According to the present invention, the injection rate can be controlled to a more preferable injection rate by performing the injection rate control together with the adjustment of the fuel injection pressure.

[0013]

FIG. 1 is an overall view of an embodiment of the present invention. The fuel is introduced from the fuel tank to the fuel supply pump via the suction passage, and is stored in a state where the pressure is increased on the common rail 51 via the discharge passage. Common rail 51
The high-pressure fuel inside is supplied to the fuel injection valve 1 (1 ′) of each cylinder via the supply passage 52, and the fuel injection valve 1 (1 ′)
The fuel is injected into the combustion chamber of the engine 50 from a plurality of injection holes provided at the tip. Further, an in-cylinder pressure sensor 53 for detecting an in-cylinder pressure is provided in each cylinder, for example, by being assembled integrally with a spark plug.

The control unit 54 receives various detection signals from sensors for detecting in-cylinder pressure, engine rotation speed, crank angle, accelerator opening, water temperature, EGR rate, and supercharging pressure. The control unit 54 searches the common rail fuel pressure, the fuel injection amount, the fuel injection rate, the number of fuel injections, and the target value of the fuel injection timing based on the accelerator opening, the engine rotation speed, and the like. In addition to setting the control opening / closing timing of the fuel injection valve so as to be the target value of the injection amount and the fuel injection timing,
Control is performed so that the fuel pressure in the common rail 51 becomes a target value.

Next, the specific structure of the fuel injection valve is shown in FIG.
This will be described with reference to FIG. In FIG. 2, the fuel injection valve 1
Is composed of a nozzle holder 2, a nozzle body 3, and an injection valve driving unit 4.
The nozzle holder 2 and the nozzle body 3 are integrated.
A needle valve slide hole 6 and a fuel reservoir 7 are formed in the nozzle body 3, and a nozzle hole 8 communicating with the fuel reservoir 7 is formed at the tip. Needle valve 9 is provided in needle valve sliding hole 6.
Large diameter portion 10 is slidably fitted. The large-diameter portion 10 of the needle valve 9 has a connecting portion 11 formed thereon, and a small-diameter portion 12 and a valve body portion 13 are integrally formed at a lower end portion.

The valve portion 13 opens and closes the seat portion X, and turns on / off the fuel injection from the nozzle hole 8. A push rod 14 is in contact with the distal end of the connecting portion 11 of the needle valve 9 and is urged by a spring 16 in a valve closing direction. The pins 17 position the nozzle body 3 and the nozzle holder 2. The push rod 14 is
It is slidably fitted in a cylinder 15 formed in the nozzle holder 2. A needle valve 9 is provided above the nozzle holder 2.
And an injection valve driving unit 4 for driving the push rod 14, and an electromagnetic valve (solenoid) is provided in the injection valve driving unit 4.
A control current is supplied through a connector section. The solenoid valve 22 is provided with a valve body 22a according to the energized state.
And opens and closes a communication passage 39 that communicates the back pressure chamber 38 of the push rod 14 with the low pressure chamber 20 on the fuel outlet 24 side.
As a result, the pressure in the back pressure chamber 38 of the push rod 14 is released. A fuel supply passage 19 for high-pressure fuel is formed in the nozzle holder 2, one end of which is connected to the inlet 18 of the nozzle holder 2, the other end of which communicates with the fuel storage chamber 7 and also communicates with the back pressure chamber 38. I do. The high-pressure fuel of the common rail 26 is supplied to the fuel storage chamber 7 and the back pressure chamber 38 via the inlet 19 and the fuel supply passage 19. The leaked fuel in the fuel injection valve 18 is returned from the fuel outlet 24 into the fuel tank. Usually, the needle valve 9 is
Although it is urged in the closing direction by the push rod 14 receiving the pressure of the back pressure chamber 38, when the energization of the solenoid valve 22 is started, the communication path 39 is opened, the pressure of the back pressure chamber 38 decreases, and the push Since the pressing force from the back of the rod 14 is reduced, the fuel pressure applied to the fuel storage chamber 7
The needle valve 9 lifts and opens, and fuel is injected. When the energization of the solenoid valve 22 is stopped, the valve body 22a closes the communication passage 39, and the pressure in the back pressure chamber 38 increases. At this time, since the pressure receiving area in the direction of pushing down the push rod 14 is large,
The needle valve 9 is pushed down against the spring 16 to close the valve, and the fuel injection stops. Therefore, the fuel injection amount and the injection timing can be freely controlled by controlling the energization interval and timing to the solenoid valve 22, and a plurality of injections can be performed by controlling the number of energizations in one cycle. The injection rate can be reduced in a pseudo manner by increasing the number of injections and decreasing the injection amount of each injection by repeating the ON / OFF of the electromagnetic valve 22 in a short cycle, and conversely, the ON / OFF of the electromagnetic valve 22 can be reduced.
By increasing the off-cycle and increasing the amount of each injection while reducing the number of injections, it is possible to artificially increase the injection rate.

Next, in FIG. 3, another fuel injection valve 1 '
Is shown. In the fuel injection valve 1 of FIG. 2, the solenoid valve 22 is disposed in the injection valve driving unit 4, but in FIG.
Piezoelectric elements 26 are arranged in a stack in the injection valve driving section 4, and power is supplied through the connector section 23.
The piezoelectric element 26 expands and contracts in accordance with the energized voltage value. A pusher 27 abuts on the piezoelectric element 26, and the pusher 27 presses the push rod 14. It is raised by 21. The injection valve driving section 4 is connected to the nozzle holder 2 by a lock nut 25. In addition,
Leaked fuel in the fuel injection valve 1 is returned to the fuel tank from the fuel outlet 24. Usually, the needle valve 9 is the push rod 1
The lift amount is controlled by controlling the energization of the piezoelectric element 26 from this state. That is, when the voltage applied to the piezoelectric element 26 is reduced, the piezoelectric element 26 contracts,
The pusher 27 is returned by the return spring 21, and the push rod 14 has a reduced pressing force from the back, so that
The needle valve 9 is controlled by the fuel pressure applied to the fuel reservoir 7.
Lifts and opens, and fuel is injected. The maximum lift amount of the needle valve 9 at this time changes according to the voltage value applied to the piezoelectric element 26, and the lift amount increases as the voltage value decreases. When the voltage applied to the piezoelectric element 26 is increased, the amount of expansion of the piezoelectric element 26 is increased, and the pusher 27,
The needle valve 9 pressed via the push rod 14 closes, and fuel injection stops. Therefore, the piezoelectric element 26
By controlling the voltage value and timing applied to the fuel cell, the fuel injection amount and injection timing can be freely controlled, and the number of times of energization in one cycle can be increased.

As described above, the needle valve lift amount can be controlled by the applied voltage value. However, by repeatedly applying the voltage, the control can be performed with the same or higher degree of freedom of the injection rate as in the fuel injector of FIG. Can be. The flowchart shown in FIG. 4 shows the injection control executed by the control unit 54 when the fuel injection valve 1 shown in FIG. 2 is used. This flow is repeated in synchronization with the engine rotation.

In step 1, the engine speed Ne, engine load Q, and cooling water temperature Tw are read as various engine operating conditions. In step 2, a basic fuel injection amount, a basic fuel injection timing, and a basic common rail pressure according to the operation state determined based on these are calculated. In step 3, the in-cylinder pressure p detected by the in-cylinder pressure sensor and the crank angle θ from the crank angle sensor are read.

In step 4, the in-cylinder pressure change rate dp / dθ is calculated from the in-cylinder pressure p and the crank angle θ.
In step 5, the magnitude of the in-cylinder pressure change rate dp / dθ is compared with a predetermined maximum in-cylinder pressure change rate dpmax, and if the in-cylinder pressure change rate dp / dθ is smaller than dpmax, this control is terminated as it is, If it is equal to or greater than dpmax, the routine proceeds to step 6, where split injection for splitting main injection is performed.

In step 7, the in-cylinder pressure change rate dp is
/ Dθ is compared with a predetermined maximum in-cylinder pressure change rate dpmax. If the in-cylinder pressure change rate dp / dθ is smaller than dpmax, the control is terminated as it is. Then, the injection start timing is set by delay correction of a predetermined amount. In step 9, it is determined whether or not the injection start timing after the retard correction is at the retard limit. When it is determined that the retard is at the retard limit, the control is terminated as it is.

On the other hand, if the injection start timing is less than the retard limit, the routine returns to step 8 and the injection start timing is again retarded. Regarding the number of times of retard correction, a number corresponding to the retard limit is set, and when the injection start timing reaches the retard limit, the control is ended regardless of the in-cylinder pressure change rate dp / dθ. The flowchart shown in FIG. 5 shows the details of the injection control executed by the control unit when the fuel injection valve shown in FIG. 3 is used.
The only difference from the first embodiment is that the initial injection rate is reduced in step 26 when the in-cylinder pressure change rate dp / dθ is determined to be equal to or greater than the maximum in-cylinder pressure change rate dpmax in step 25. That is, in the first embodiment, the injection rate is reduced artificially by the split injection, whereas in the second embodiment, the initial injection rate is set to be reduced to a desired initial injection rate by controlling the voltage applied to the piezoelectric element 26.

As described above in the first and second embodiments,
By controlling the fuel injection pattern in accordance with the in-cylinder pressure change rate dp / dθ, a sudden pressure change can be suppressed, and combustion noise can be reduced. Although the combustion noise reduction effect can be obtained by the conventional pilot injection control, the effect can be further enhanced by using the present invention and the pilot injection control together. When the pilot injection control is used together, the control according to the present invention is performed subsequent to the pilot injection.

As a means for calculating the in-cylinder pressure change rate, it is also possible to use a vibrometer or an ion sensor or the like and convert the detected value of the combustion state in the cylinder into a pressure change to obtain dp / dθ. Next, specific injection patterns of the first and second embodiments and their effects will be described.

FIG. 6 shows an example of an in-cylinder pressure waveform and a pressure change rate obtained in a normal operation. When normal fuel injection (in this example, only main injection) is performed, combustion starts at the timing indicated by the arrow in the figure, and the air-fuel mixture in the premixed state during the ignition delay period burns rapidly. As a result, the in-cylinder pressure rapidly increases, and the pressure change rate dp / dθ increases. Therefore,
In the present invention, injection control is performed such that the pressure change rate dp / dθ is equal to or less than the maximum in-cylinder pressure change rate dpmax shown in the figure. The maximum in-cylinder pressure change rate dpmax varies depending on operating conditions and is set according to the supercharging pressure and the required pressure.

FIG. 7 shows a specific control example. (A) shows a divided main injection, in which the injection rate at the initial stage of fuel injection is reduced by multiple injections. (B) is an example in which the injection start timing is retarded from the example of (a), and the effect of suppressing rapid combustion is higher than (a). (C) shows a control example in which the injection rate can be variably controlled as in the fuel injection valve shown in FIG. 3, and shows the injection rate at the beginning of fuel injection. The injection rate has been reduced. (D)
This is an example in which the injection start timing is retarded with respect to the example of (c). Even when the fuel injection valve shown in FIG. 2 is used, when the rail pressure can be variably controlled, so-called boot-type injection becomes possible as shown in FIG. It becomes possible. By controlling the rail pressure and controlling the period indicated by the arrow in the drawing, the initial injection rate can be controlled.

FIG. 8 shows an example of the in-cylinder pressure progress and the pressure change rate when the injection control of the present invention is actually performed. The dotted line indicates the waveform when the control is not performed, and the solid line indicates the waveform when the control is performed. The injection pattern corresponds to the case where the number of injections in FIG. 7A is increased. As is clear from the graph, it is possible to suppress rapid combustion by performing the control of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a sectional view showing the internal structure of a fuel injection valve used in the first embodiment.

FIG. 3 is a sectional view showing an internal structure of a fuel injection valve used in a second embodiment.

FIG. 4 is a flowchart of a fuel injection control routine according to the first embodiment;

FIG. 5 is a flowchart of a fuel injection control routine according to a second embodiment.

FIG. 6 is a diagram showing characteristics of in-cylinder pressure and in-cylinder pressure change rate during normal operation.

FIG. 7 is a diagram showing changes in various states according to the first and second embodiments of the present invention.

FIG. 8 is a diagram showing the characteristics of the in-cylinder pressure and the in-cylinder pressure change rate according to the first embodiment in comparison with the non-controlled state.

[Explanation of symbols]

 1, 1 'Fuel injection valve 9 Needle valve 22 Solenoid valve 26 Piezoelectric element 50 Engine 51 Common rail 53 Swirl control valve 54 Control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 45/04 F02M 45/04 47/00 47/00 CE 47/02 47/02 51/06 51 / 06 N 55/02 350 55/02 350E 61/20 61/20 MF term (reference) 3G066 AA07 AB02 AC09 AD02 BA13 BA22 CB12 CC06T CC08T CC08U CC14 CC64T CC64U CC66 CC67 CC68U CD25 CD26 CE13 CE22 CE27 DA01 DA04 DA06 DA09 DC04 DC05 DC06 DC09 DC14 DC17 DC18 3G084 AA01 BA11 BA13 BA14 BA15 DA39 EA11 EC01 EC03 FA00 FA10 FA12 FA20 FA21 FA33 FA37 3G301 HA02 HA04 HA11 HA13 JA37 LB06 LB16 MA11 MA18 MA26 MA27 PA16Z PB06Z PC01Z PD15Z PE01Z PE08Z

Claims (7)

[Claims] A fuel injection means for directly injecting fuel into a combustion chamber of the engine; an in-cylinder pressure detecting means for detecting an in-cylinder pressure of the engine; and a cylinder pressure change rate based on the cylinder pressure detection value. An in-cylinder pressure change rate calculating means for calculating the in-cylinder pressure change rate, an injection rate control means for reducing the initial as compared to the latter half of the fuel injection period as the in-cylinder pressure change rate increases, A fuel injection control device for a diesel engine, comprising: 2. The fuel injection control device for a diesel engine according to claim 1, wherein the injection rate control means delays the fuel injection timing as the in-cylinder pressure change rate increases. 3. The injection rate control means injects fuel in a greater number of divisions during the fuel injection period as the in-cylinder pressure change rate increases, and includes:
The fuel injection control device for a diesel engine according to claim 1 or 2, wherein the injection amount of the subsequent injection is increased. 4. The fuel injection means includes a needle valve for injecting fuel by a lift, and a fuel injection valve having a solenoid for lifting the needle valve while a command voltage is applied. The means controls the number of injections by the number of times the command voltage is applied during the fuel injection period, and controls the injection time by the application time for each application of the command voltage divided into a plurality of times. The fuel injection control device for a diesel engine according to claim 3, wherein 5. The fuel injection means includes a needle valve for injecting fuel at a higher injection rate as the lift amount increases, and a piezoelectric element for increasing the lift amount of the needle valve as the applied command voltage increases. 3. The fuel injection control device for a diesel engine according to claim 1, wherein the fuel injection control device comprises a fuel injection valve. 6. The fuel injection control device according to claim 1, wherein, when the in-cylinder pressure change rate exceeds a predetermined value, the injection rate control means decreases the injection rate in the initial period as compared to the latter period in the fuel injection period. The fuel injection control device for a diesel engine according to any one of claims 1 to 5. 7. The fuel injection pressure can be adjusted by adjusting the fuel pressure in a common rail, and the injection rate control means controls the injection rate while adjusting the fuel injection pressure. The fuel injection control device for a diesel engine according to any one of claims 1 to 6.