JPH1182220A - Fuel injection controller of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the injection rating characteristics of a common-rail fuel injection controller of a diesel engine. SOLUTION: An opening area A of an overflowing passage 39 making a flow of fuel in a back pressure chamber 38 overflow into a low pressure source is formed to be larger than an opening area B of a fuel inlet passage 41 inducing high pressure fuel out of a common rail into this back pressure chamber 38 faced to the back of a push rod 14 connected to a needle valve of a fuel injection valve, and on the other hand, a lift characteristic of a valve element 40 of a solenoid valve opening or closing an opening part of the overflowing passage 39 is turned to such a characteristic that a variation factor in the opening area of the overflowing passage 39 becomes enlarged according to an increment of lift amount. With this constitution, while an initial injection rate is held down to smallness, the latter period injection rate is largely securable, and further, spill performance is also improved.

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 fuel accumulator (hereinafter referred to as a fuel pressure accumulator).
(Referred to as common rail) type fuel injection control device,
The present invention relates to a technique for increasing a spill speed while suppressing an initial injection rate, suppressing combustion noise and NOx, and reducing particulates.

[0002]

2. Description of the Related Art As a fuel injection control device for a diesel engine, there is a common rail type fuel injection control device as disclosed in Japanese Patent Application Laid-Open No. 62-258160. This is done by accumulating high-pressure fuel pumped from a fuel pump into a kind of surge tank called a common rail, and controlling it to a desired pressure based on a signal from a pressure sensor attached to the common rail. The fuel is sent to the fuel injection valve via the injection pipe, the back pressure of the needle valve is controlled by the solenoid valve, the opening and closing control of the fuel injection valve is performed, and the fuel injection is controlled.

[0003]

In the common rail type fuel injection control device, the back pressure by the fuel pressure applied to the needle valve of the fuel injection valve is controlled by opening and closing the fuel injection valve by opening and closing a solenoid valve. Therefore, the relationship between the opening area B of the fuel inlet passage to the back pressure chamber of the needle valve and the opening area A of the fuel overflow passage opened and closed by the solenoid valve needs to be A> B. Was. That is, when A ≦ B, the fuel inflow in the back pressure chamber becomes larger than the fuel outflow, so that the needle valve cannot be opened and fuel injection becomes impossible.

On the other hand, in a diesel engine, it is ideal to realize an injection rate waveform as shown in FIG. That is, by reducing the initial injection rate, the combustion noise is reduced, and the generation of NOx is suppressed, and the generation of smoke is suppressed by increasing the spill speed to improve the cutoff of the injection. In general, the injection performance of a diesel engine is substantially determined by the initial injection rate characteristic at the beginning of injection and the spill speed (injection rate reduction rate per unit time) that determines the cutoff of injection at the end of injection. The initial injection rate is determined by the rising speed of the needle valve, and the spill speed is determined by the falling speed of the needle valve.

In the common rail type fuel injection control device, the rising speed of the needle valve is determined by how fast the high pressure fuel in the back pressure chamber leaks from the overflow passage. It is determined by the area A of the overflow passage. On the other hand, the lowering speed of the needle valve is determined by the speed at which the high-pressure fuel is fed into the back pressure chamber, and is therefore determined by the area B of the fuel inlet passage.

In the conventional common rail type fuel injection control device, the area A, B
Is small, the initial injection rate and spill speed that determine the injection characteristics are uniquely determined only by these areas A and B. However, as described above, since the relationship between the two areas is A> B, when the area B is reduced in accordance with the reduction of the area A to suppress the initial injection rate as shown in FIG. If the area A is enlarged in accordance with the enlargement of the area B in order to increase the spill speed, the initial injection rate also increases,
It was not possible to achieve both performances.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and aims at achieving both desired performance of noise, output and exhaust emission while suppressing the initial injection rate and increasing the spill speed. It is an object of the present invention to provide a diesel engine fuel injection control device capable of obtaining performance.

[0008]

According to a first aspect of the present invention, a fuel discharged from a fuel injection pump is supplied to a fuel accumulator, and a fuel pressure in the fuel accumulator is set according to an engine operating state. While the pressure is controlled by feedback, the high-pressure fuel in the fuel accumulator acts on the needle valve of the fuel injection valve mounted on the combustion chamber of each cylinder of the engine in the valve opening direction and the fuel reservoir operates in the valve closing direction. A fuel injection control of a diesel engine that controls the fuel injection by opening and closing the needle valve by opening and closing an overflow passage connecting the back pressure chamber and the fuel low pressure source with an electromagnetic valve while guiding the fuel injection to the back pressure chamber. The apparatus is characterized in that the changing speed of the opening area of the overflow passage when the solenoid valve is lifted is set to be variable according to the lift amount of the solenoid valve.

According to the first aspect of the invention, in a region where the lift amount of the solenoid valve is small, the rate of change of the opening area of the overflow passage is reduced, so that the initial injection rate can be suppressed low, and the lift of the solenoid valve can be reduced. By increasing the rate of change of the opening area of the overflow passage in the region where the amount is large, the opening area of the overflow passage is reduced in a short time when the solenoid valve is closed, thereby increasing the closing speed of the needle valve, that is, the spill speed. it can.

According to a second aspect of the present invention, the valve body of the solenoid valve and the overflow passage are arranged such that the rate of change of the opening area of the overflow passage increases in accordance with an increase in the lift amount of the solenoid valve. Are formed. According to the invention according to claim 2, when the lift amount of the solenoid valve is small, the initial injection rate can be suppressed low because the rate of increase of the opening area of the overflow passage with respect to the increase of the lift amount is small, and when the lift amount is large. As the lift amount increases, the opening area of the overflow passage sharply increases, so that the late injection rate can be sufficiently increased, and when the solenoid valve is closed, the opening area of the overflow passage sharply decreases. Therefore, the spill speed can be set sufficiently high.

The invention according to claim 3 is characterized in that the solenoid valve is arranged at a fuel outlet from the back pressure chamber in the fuel injection valve to the overflow passage. Claim 3
According to the invention according to the invention, by providing the solenoid valve in the vicinity of the back pressure chamber, it is possible to change the pressure in the back pressure chamber with high responsiveness and to enhance the injection control accuracy, and to install the solenoid valve inside the fuel injection valve. By providing such a device, the entire apparatus can be made compact.

Further, the invention according to claim 4 is characterized in that an opening area of the overflow passage is larger than an opening area of a fuel inlet passage for guiding high-pressure fuel from the fuel accumulator to the back pressure chamber. I do. According to the fourth aspect of the present invention, the amount of fuel overflow through the overflow passage can be made larger than the amount of fuel introduced into the back pressure chamber through the fuel inlet passage. The needle valve of the valve can be opened,
Fuel injection can be performed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an overall configuration of a diesel engine fuel injection control device according to one embodiment of the present invention. FIG.
In the above, the fuel injection valve 1 provided in the combustion chamber of each cylinder of the engine is connected via an injection pipe 27 to a fuel accumulation chamber common to the cylinders, a so-called common rail 26. A high pressure supply pump 30 is connected to the common rail 26 via a supply pipe 28 and a check valve 29. This high pressure supply pump 30
Is for increasing the pressure of the fuel sucked from the fuel tank 31 via the fuel feed pump 33 via the fuel filter 32 to a predetermined high pressure, and controlling the fuel to a predetermined high pressure. That is, the drive shaft 34 having the cam lobe rotates in synchronization with the rotation of the engine (not shown), the piston in the high pressure supply pump 30 reciprocates, the fuel from the fuel feed pump 33 is pressurized, and the common rail 26 Supplied to Further, a pressure sensor 37 for detecting the fuel pressure in the common rail 26 is provided on the common rail 26, and the high-pressure supply pump 30 includes a discharge amount control solenoid valve 35 for controlling the fuel pressure in the common rail. I have.

The electronic control unit 36 includes the pressure sensor 37
The fuel pressure in the common rail 26 is set in advance according to the engine operating state determined from the detected values of the engine load and the rotation speed while driving the discharge amount control solenoid valve 35 based on the detected value of By controlling the discharge amount to be an optimum value and controlling the opening and closing of a solenoid valve, which will be described later, mounted inside the fuel injection valve 1, the optimum injection amount and injection timing determined according to the engine operating state. Is controlled so that

Next, the internal structure of the fuel injection valve 1 will be described with reference to FIG. In FIG. 2, the fuel injection valve 1
Comprises a nozzle holder 2, a nozzle 3, and a valve driver 4,
The nozzle holder 2 and the nozzle 3 are integrally connected by a retaining nut 5. A needle valve slide hole 6 and a fuel reservoir 7 are formed in the nozzle 3, and a nozzle hole 8 communicating with the fuel reservoir 7 is formed at the tip of the nozzle 3. The large diameter portion 10 of the needle valve 9 is slidably fitted in the needle valve sliding hole 6. The large diameter portion 10 of the needle valve 9 has a connecting portion
11, a small diameter portion 12 and a valve body portion 13 are integrally formed at a lower end portion. Then, the seat portion X is opened and closed by the valve body portion 13, and the injection from the nozzle hole 8 is turned on / off.

A push rod 14 is integrally connected to the distal end of the connecting portion 11 of the needle valve 9.
Are slidably fitted in a cylinder 15 formed in the nozzle holder 2. The needle valve 9 is urged in the closing direction by a spring 16. The pin 17 positions the nozzle 3 and the nozzle holder 2. Nozzle holder 2
The valve drive unit 4 for driving the needle valve 9 and the push rod 14 is disposed above the nosepiece. An electromagnetic valve 22 is built in the injection valve driving section 4, and electric power is supplied through a connector section 23. The solenoid valve 22 opens and closes an overflow passage 39 that connects a back pressure chamber 38 facing the rear end of the push rod 14 and a low pressure source (fuel tank) by a valve body 40, and the fuel in the back pressure chamber 38 Control of the needle valve 9 and on / off control of the fuel injection. FIG. 3 shows the solenoid valve 22 according to the present invention in an enlarged shape at the tip end of the needle valve. As for the shape, as the lift of the valve body 40 increases, the overflow passage 39
The opening area at the maximum lift is increased, and the opening area at the time of the maximum lift is set to be equal to the opening area of the overflow passage 39. FIG. 4 shows a change in the opening area of the overflow passage 39 with respect to the lift amount of the valve body 40 at this time, as compared with the conventional example.

The valve control drive unit 4 includes a lock nut 25
To the injection nozzle holder 2. Also,
Leaked fuel in the fuel injection valve 1 is returned to the fuel tank from the fuel outlet 24. A fuel supply passage 19 is formed in the nozzle holder 2, one end of which is opened on the surface of the nozzle holder 2, connected to the injection pipe 27 via an inlet 18, and the other end is connected to the fuel storage chamber 7. Is communicated to. In addition, a fuel inlet passage 41 that connects the fuel supply passage 19 and the back pressure chamber 38 is formed.

Therefore, the high-pressure fuel in the common rail 26 is supplied to the fuel storage chamber 7 through the inlet 18 and the fuel supply passage 19, and the fuel supply passage 1
9. The fuel is supplied to the back pressure chamber 38 via the fuel inlet passage 41. Here, the opening area A of the overflow passage 39 is formed to be larger than the opening area B of the fuel inlet passage 41.
Normally, the needle valve 9 is urged in the closing direction by the push rod 14. From this state, the solenoid valve 22 is controlled, and when the high-pressure fuel in the back pressure chamber 38 overflows, the fuel accumulation chamber 7 is closed. The pressure balance with the back pressure chamber 38 is reversed and the urging force of the spring 16 is overcome, so that the needle valve 9 and the push rod 14 move upward and fuel is injected.

As described above, according to the present invention, as the lift of the valve body 40 of the solenoid valve 22 increases, the overflow path 39
Since the opening area of the overflow passage 39 is small at the initial stage of the lift, the needle valve 9 moving integrally with the push rod 14 is gradually lifted at the initial stage of the injection. Since the rate is suppressed and the opening area increases sharply thereafter, the injection rate in the latter half of the injection can be made sufficiently large. Also, at the time of spill, when the solenoid valve 22 starts to close, the opening area of the overflow passage 39 sharply decreases, so that the spill speed can be sufficiently increased.

Further, even if the opening area of the fuel inlet passage 41 to the back pressure chamber 38 is increased to improve the spill performance, and the opening area of the overflow passage 39 is made larger than that, the lift of the solenoid valve described above is increased. The configuration of the characteristics makes it possible to suppress the initial injection rate. In this way, an injection rate characteristic close to the ideal injection rate characteristic as shown in FIG. 5 is obtained, and by suppressing the initial injection rate, burning noise and NOx can be reduced, and at the same time, spill performance is improved. Thereby, the amount of smoke emission can also be reduced.

The pilot injection can be realized by opening and closing the solenoid valve 22 twice per cycle of each cylinder. Also, the actual injection rate can be obtained from the signal of the pressure sensor 37 and the signal to the solenoid valve 22. Can be calculated.

[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 the fuel injection valve of the embodiment.

FIG. 3 is an enlarged view of a part a in FIG. 2;

FIG. 4 is a diagram showing the inertia between the lift amount of the electromagnetic valve and the opening area of the overflow passage in the embodiment, as compared with the conventional case.

FIG. 5 is a view showing ideal injection rate characteristics.

FIG. 6 is a diagram showing injection rate characteristics according to a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel injection valve 4 Valve drive 7 Fuel reservoir 9 Needle valve 26 Common rail 38 Back pressure chamber 39 Overflow passage 40 Valve element 41 Fuel inlet passage

Claims (4)

[Claims] A fuel discharged from a fuel injection pump is supplied to a fuel accumulator and a fuel pressure in the fuel accumulator is feedback-controlled to a pressure set in accordance with an engine operating state. The high-pressure fuel guides the needle valve of the fuel injection valve mounted in the combustion chamber of each cylinder of the engine to a fuel accumulation chamber acting in the valve opening direction and a back pressure chamber acting in the valve closing direction. A fuel injection control device for a diesel engine that controls fuel injection by opening and closing the needle valve by opening and closing an overflow passage connecting to a low fuel pressure source with an electromagnetic valve, wherein the overflow passage when the electromagnetic valve is lifted is provided. A fuel injection control device for a diesel engine, characterized in that a changing speed of an opening area of the fuel injection valve is set to be variable according to a lift amount of the solenoid valve. 2. The valve body of the solenoid valve and the opening of the overflow passage are formed so that the rate of change of the opening area of the overflow passage increases with an increase in the lift amount of the solenoid valve. The fuel injection control device for a diesel engine according to claim 1, wherein: 3. The diesel engine according to claim 1, wherein the solenoid valve is disposed at a fuel outlet from the back pressure chamber in the fuel injection valve to the overflow passage. Engine fuel injection control device. 4. An opening area of the overflow passage is larger than an opening area of a fuel inlet passage for guiding high-pressure fuel from the fuel pressure accumulating chamber to the back pressure chamber. The fuel injection control device for a diesel engine according to any one of the above.