JP2000130283A - Fuel injecting device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize good combustion characteristics by improving fuel spray. SOLUTION: This fuel injecting device is provided with a fuel pressure accumulating chamber 9 for accumulating fuel in the high pressure state, pressurized by a fuel supplying pump 1, and an injector 14 for injecting high-pressure fuel from the fuel pressure accumulating chamber 9. The injecting device is provided with a selector valve 18 for selectively connecting or shutting a fuel passage 16 for linking the injector 14 and the fuel pressure accumulating chamber 9 to each other, and a controller 50 for controlling a pressure control valve 25 of the injector 14 and the selector valve 18. The controller 50 closes the selector valve 18 before fuel injection and opens the pressure control valve 25 to hold the pressure chamber to low pressure. It opens the selector valve 18 in fuel injection starting timing to inject fuel. It closes the pressure control valve 25 in fuel finishing timing, and increases the pressure of the pressure chamber to high pressure to finish fuel injection, and then closes the selector valve 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for a fuel storage type diesel engine.

[0002]

2. Description of the Related Art As a fuel injection device for a diesel engine, there has been known a fuel injection device in which high-pressure fuel is stored in a pressure accumulating chamber, and the pressurized fuel is injected from an injector at the fuel injection timing. The configuration of the injector is proposed in Japanese Patent Application Laid-Open No. Hei 9-58811.

The configuration of this injector will be described with reference to FIG.

[0004] The high-pressure fuel in the accumulator is guided from the supply passage 101 to the nozzle chamber 102, and a part thereof passes through the filling orifice 106 and the pressure chamber 1 above the nozzle piston 104.
It is also led to 05. When the discharge orifice 108 connecting the pressure chamber 105 to the drain side is closed by the solenoid valve 107, the nozzle piston 1 receiving this fuel pressure
The needle valve 103 is pushed and seated by 04, and no fuel is injected. The pressure receiving area of the nozzle piston 104 is larger than the pressure receiving area of the needle valve 103.

When the solenoid valve 107 opens from this state,
The pressure in the pressure chamber 105 is reduced via the discharge orifice 108, so that the needle valve 103 is lifted upward by the fuel pressure acting on the nozzle chamber 102, and fuel is injected.

When the solenoid valve 107 is closed, the pressure chamber 105
Is filled with high-pressure fuel via a filling orifice 106,
The needle valve 103 is pushed down and seated by the nozzle piston 104 having a larger pressure receiving area than the needle valve 103, and the fuel injection is stopped.

The return spring 109 prevents the fuel in the nozzle chamber 105 from leaking into the combustion chamber when the engine is stopped or the like. When the engine is operating, the hydraulic pressure applied to the needle valve 103 and the nozzle piston 104 is reduced. As a result, the needle valve 103 and the nozzle piston 104 always move integrally.

In such an injector, the pressure chamber 10
5 and the force in the valve opening direction which is the product of the pressure in the nozzle chamber 104 and the pressure receiving area of the needle valve 103, and the force in the valve opening direction which is the product of the pressure in the nozzle chamber 102 and the pressure receiving area of the needle valve 103. The movement of the needle valve 103 is determined. In this case, since the nozzle chamber 102 is always in communication with the accumulator (not shown) via the supply passage 101, the pressure is almost constant, whereas the pressure in the pressure chamber 105 is increased by opening and closing the solenoid valve 107. Change.

The hydraulic pressure received by the nozzle piston 104 is
When the solenoid valve 107 is opened, it depends on the effective flow area of the filling orifice 106 and the discharge orifice 108 and the pressure receiving area of the nozzle piston 104. When the solenoid valve 107 is closed, the effective flow area of the filling orifice 106 and the nozzle piston It is affected by the pressure receiving area 104. Thus, by changing three parameters of the effective flow passage area of the filling orifice 106 and the discharge orifice 108 and the diameter of the nozzle piston 104, the ascending and descending speeds of the needle valve 103,
That is, the fuel injection rate can be changed.

[0010] The fuel injection rate has a gentle rising slope for reducing combustion noise and suppressing NOx emission due to the reduction of the injection amount during the ignition delay period at the beginning of the injection. Because it is common to increase the slope on the descending side for suppression (see "Internal Combustion Engine" Vol.
31 No.393 1992.7 p.21 to p.29), the ascent speed of the needle valve 16 at the time of lift is reduced and the descent speed is increased by matching of the above three parameters.

[0011]

The situation of the fuel spray has a great influence on the combustion state. Therefore, the present inventor has studied what the spray sprayed from the injector of the accumulator type fuel injector actually looks like. Upon investigation, the following findings were obtained.

To explain this, in the above-mentioned injector, the needle valve 103 has a low ascending speed, so that the needle valve lift is low at the beginning of the injection, and the fuel has passed at a high speed through the very narrow clearance of the nozzle seat portion. Later, it flows into the nozzle orifice.

FIG. 7 is a cross-sectional view of the nozzle tip. This type has a shape in which the nozzle hole 109 is blocked by the nozzle seat portion 109 of the needle valve 103 when the needle valve 103 is seated. Covered Orifice) type.

Here, looking at the fuel flow velocity distribution in a cross section perpendicular to the axis of the injection hole 110, FIG.
As shown in FIG. 7, a weak flow symmetrical with respect to the central axis of the needle valve 103 is generated. This is because the fuel flows from the nozzle sheet portion 109 to the upper portion of the injection hole 110 first.

However, in an actual nozzle,
The needle valve 103 is slightly eccentric due to the play of the needle valve sliding portion and the problem of manufacturing accuracy. For example, FIG.
When the eccentricity to the left side is generated as shown in the arrow view of the line A), a symmetrical circumferential flow around the needle valve 103 from the narrow space to the wide space in the nozzle seat portion 109 is obtained. (Indicated by the arrow) occurs. In this case, as shown in FIG. 10, a strong swirling flow is generated along the inner circumference inside the injection holes 110a and 110b located at the portion where the flow is fast.

Such a swirling flow in a plane perpendicular to the axis of the injection hole becomes strong when the needle valve lift is small and when the nozzle chamber pressure is high. This is because the narrower the nozzle seat portion 109, the higher the fuel flow rate in the circumferential direction of the nozzle seat portion 109, and the higher the pressure in the nozzle chamber 102, the faster the fuel flow speed in the nozzle seat portion 109.

When the swirling flow in the plane perpendicular to the axis of the injection hole is large, the spray cone of the fuel has a wide spray cone angle for the injection rate and the penetration is weak, but the atomization is promoted. Spray (that is, spray with good ignitability). Such a phenomenon is particularly remarkable in a VCO type nozzle.

Such a fuel spray has good ignitability and promotes evaporation and mixing with the surrounding air, so that the ignition delay period is shorter than that of a conventional spray of a jerk type fuel injection device (details will be described later). Therefore, there is an advantage that the amount of premixed combustion at the beginning of combustion is reduced, and combustion noise and NOx emission are suppressed. However, on the other hand, in the operating range where the excess air ratio is small, such as in the high load range, the premixed combustion ratio is reduced, and in addition, near the center of the combustion chamber where the flow is weak, the spray that is initially injected and the weak spray of the penetration remains. Therefore, there is a demerit that the generation of smoke increases.

The above is the knowledge obtained by the inventor for the first time.

On the other hand, in the jerk type fuel injection device, the fuel is rapidly pressurized by a plunger, the generated pressure wave is guided to the nozzle chamber through the fuel injection pipe, and the fuel pressure in the nozzle chamber is changed to a substantially mountain shape. The pressure lifts the needle valve against the force of the return spring in the needle valve seating direction,
It is configured to inject fuel.

In such a jerk type fuel injection device,
Due to the low nozzle chamber pressure in the early stage of injection and the short period during which fuel is injected with the low needle valve lift due to the rapid lift of the needle valve, there is little smoke emission in the high load range, but combustion There is a demerit that noise and NOx emission are large. In addition, since the ignitability is lower than that of the fuel spray obtained by the pressure accumulating type fuel injection device, it is necessary to advance the fuel injection timing more in order to suppress misfire particularly in the cold state, and the NOx emission in the cold state is large. There is also a disadvantage.

As a method for simultaneously reducing NOx and smoke or fine particles in exhaust gas, there is a method of performing low-temperature premix combustion (see Japanese Patent Application Laid-Open No. 7-4287).

In this method, the fuel is completely injected during the ignition delay period, and the fuel is burned at a low temperature mainly by the premixed combustion. In addition to the simultaneous reduction of exhaust particulates and NOx, there is an effect of reducing combustion noise. In order to realize such combustion, the intake oxygen concentration is reduced by EGR, the combustion speed is appropriately reduced, and the fuel injection timing is delayed to around TDC. In addition, for such combustion, it is convenient that the ignition delay period is appropriately long. In this regard, in the case of the spray having good ignitability as obtained by the above-described pressure accumulating type fuel injection device, the ignition delay period is long. Because it is short and it is difficult to inject all fuel during the ignition delay period,
There has been a problem that the operating range where simultaneous reduction of exhaust particulates and NOx by low-temperature premixed combustion is narrowed.

As described above, each of the accumulator type and the jerk type fuel injection devices has advantages and disadvantages depending on the operating conditions due to the difference in the quality of the fuel spray. Note that the quality of the fuel spray refers to the particle size of the spray, the spray cone angle, and the penetration in the early stage of the injection, and these have a great effect on the ignition delay period and the smoke emission, and the engine operation as described above. The optimum ignition delay period changes according to the conditions.

The present invention solves such a problem by making it possible to variably control the quality of the fuel spray to reduce combustion noise, N
The purpose is to suppress Ox emissions and smoke emissions.

[0026]

According to a first aspect of the present invention, there is provided a fuel accumulator for storing fuel pressurized by a fuel supply pump in a high pressure state, and a high pressure fuel from the fuel accumulator is controlled by a pressure control valve. A fuel injection device for a diesel engine including an injector that injects via a valve that opens and closes in accordance with the pressure of a pressure chamber, a switching valve that selectively communicates and shuts off a fuel passage connecting the injector and the fuel accumulator chamber; ,
A controller for controlling the pressure control valve and the switching valve, the controller closing the switching valve before fuel injection, and opening the pressure control valve to maintain the pressure chamber at a low pressure, At the injection start timing, the switching valve is opened to perform fuel injection, and at the injection termination timing, the pressure control valve is closed, the pressure chamber is set to a high pressure, and the fuel injection is terminated, and then the switching valve is closed. It is configured as follows.

According to a second aspect of the present invention, there is provided a fuel accumulator for storing fuel pressurized by a fuel supply pump in a high pressure state, and a high pressure fuel from the fuel accumulator according to the pressure of a pressure chamber controlled by a pressure control valve. A fuel injection device having an injector that injects through a valve that opens and closes, a switching valve that selectively communicates and shuts off a fuel passage connecting the injector and the fuel accumulator, and a pressure control valve. A controller for controlling the switching valve, the controller closing the switching valve before fuel injection, opening the pressure control valve to maintain the pressure chamber at a low pressure, and at the fuel injection start timing Opening the switching valve to perform fuel injection, closing the pressure control valve at the end of injection to raise the pressure chamber to a high pressure, terminating fuel injection, and then closing the switching valve. In the injection mode, while holding the switching valve open, the pressure control valve is opened at the fuel injection start timing to perform the fuel injection at a low pressure in the pressure chamber, and the pressure control valve is closed at the injection end timing. Thus, it is possible to switch to a second injection mode in which the pressure chamber is set to a high pressure and fuel injection is stopped.

In a third aspect based on the first or second aspect, the controller opens and closes the pressure control valve for an extremely short time after the end of fuel injection in the first injection mode.

According to a fourth aspect of the present invention, in the first to third aspects, a needle valve which lifts and opens the injection hole when the injector receives high fuel pressure, a spring which biases the needle valve in a closing direction, A pressure chamber into which the fuel pressure is guided, and a piston that presses the needle valve in an opening direction according to the pressure of the pressure chamber,
It has a spring for urging the piston in the direction opposite to the valve closing direction of the needle valve, and a pressure control valve for opening and closing the drain flow path of the pressure chamber to adjust the pressure.

According to a fifth aspect of the present invention, in the first to fourth aspects, the switching valve lifts and opens when receiving a high fuel pressure, and a pressing chamber to which the fuel pressure is guided. A piston for pressing the sliding valve in the valve closing direction in accordance with the pressure in the pressing chamber; and a control valve for adjusting the pressure in the pressing chamber.

[0031]

According to the first aspect of the present invention, before the fuel injection, the switching valve is closed and the pressure control valve is opened to set the pressure chamber to a low pressure, and the switching valve is opened at the fuel injection start timing. Then, the high-pressure fuel acts on the needle valve, and at this time, the pressure control valve remains open, and the pressure in the pressure chamber is low, so that the needle valve is rapidly lifted with a rapid rise in fuel pressure, similar to the jerk type fuel injection. Due to the strong penetration, spraying is improved, and the generation of smoke can be suppressed even during high-load operation.

Further, the fuel injection pressure can be freely controlled by adjusting the fuel pressure in the accumulator, and good combustion can be ensured in a wide operating range.

When the pressure control valve is closed at the end of the fuel injection, the pressure in the pressure chamber becomes high, and the needle valve can be quickly pushed down to stop the fuel injection without fail.

In the second invention, the fuel injection is switched between the above-described first fuel injection mode, ie, the first fuel injection mode capable of suppressing the emission of smoke under a high load, and the second fuel injection mode different from this. Can be

In the second injection mode, the pressure control valve is opened and closed while the switching valve is kept open. When the pressure in the pressure chamber is reduced by opening the pressure control valve, the needle valve is lifted,
When the high-pressure fuel is injected and the pressure in the pressure chamber is increased by closing the pressure control valve, the needle valve is pressed by the piston, the valve is closed, and the fuel injection is stopped. So in this case,
A fuel spray having good ignitability similar to that of the conventional pressure-accumulation fuel injection can be obtained, and combustion noise and NOx can be reduced at low engine load and low engine speed.

In this way, for example, the fuel injection characteristics can be easily switched according to the operating conditions, and the optimum combustion state can be controlled according to the demand.

According to the third aspect of the present invention, the pressure in the pressure chamber and the nozzle chamber can be reliably reduced before the next fuel injection even at the time of high rotation, and stable fuel injection characteristics can be secured.

In the fourth aspect of the present invention, the piston is urged in the needle valve lift direction by the spring. Therefore, when the switching valve is opened and high-pressure fuel is supplied while the pressure control valve is held open, The needle valve can be lifted quickly, and the stronger penetration can improve the smoke characteristics, especially at high loads.

According to the fifth aspect, the fuel pressure can be used for opening and closing the switching valve, and when the pressure control valve is constituted by an electromagnetic valve or the like, the drive circuit thereof can be downsized.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration of a fuel supply system, and FIG. 2 shows a schematic sectional view of an injector. The fuel supply pump 1 includes a plunger 3 that reciprocates by a cam 2 that is driven to rotate in synchronization with the rotation of the engine. As the plunger 3 reciprocates, the fuel in the fuel tank 4 is sucked from the suction passage 6 and the check valve is provided. The pressure is discharged to the discharge passage 5 having the pressure 8 and stored in the pressure accumulating chamber 9 in a high pressure state.

In order to control the fuel pressure in the accumulator 9, an effective stroke control valve 7 is provided in the suction passage 6. The effective stroke control valve 7 remains open during the suction stroke of the plunger 3, but is closed during the compression stroke of the plunger 3, and the closing of the valve starts the fuel pumping during the valve closing period in the compression stroke. Keeps fuel pumping. Therefore, the pump discharge amount and, consequently, the fuel pressure of the accumulator 9 are determined in accordance with this.

In order to control the fuel pressure in the accumulator 9,
A controller 50 for controlling opening and closing of the effective stroke control valve 7 is provided. The controller 50 receives each detection signal from the pressure sensor 10 for detecting the fuel pressure in the accumulator 9, the accelerator opening sensor 12, the engine speed sensor 13, and the fuel injection cylinder discriminating sensor 15. The closing period of the effective stroke control valve 7 is adjusted so that the target fuel pressure set according to the operation state and the fuel pressure in the accumulator 9 match. For example, when the stored fuel pressure is lower than the target pressure, the closing period of the effective stroke control valve 7 is extended so as to increase the amount of fuel pumped by the plunger 3, and conversely, when the fuel pressure is higher, the pumping amount is reduced. Thus, the valve closing period is shortened.

The target pressure is searched according to a map determined in advance according to the operating state of the engine.

Next, the configuration of the injector 14 will be described with reference to FIG.

The fuel passage 16 of the injector 14 is connected to the high-pressure supply passage 11 of the accumulator 9. Fuel passage 16
A first solenoid valve 18 as a switching valve is interposed in the middle, and when the solenoid valve 18 is opened, the fuel passage 16 is connected to the internal passage 17, high-pressure fuel is introduced, and when the solenoid valve 18 is closed, High pressure fuel is shut off.

The internal passage 17 communicates with the nozzle chamber 27 and with the pressure chamber 22 via the filling orifice 23. The needle valve 19 that opens and closes the injection hole 27a of the nozzle chamber 27 includes:
It comes into contact with the nozzle piston 21 via the pressing member 20.
Here, the diameter of the nozzle piston 21 is the needle valve sliding portion 19a.
, That is, the pressure receiving area is set large. The pressure chamber 22 is provided with a discharge orifice 24 in a drain passage connected to the low pressure side.
Is opened and closed by a second solenoid valve 25 as a pressure control valve.

The pressing member 20 is urged by a return spring 26 to prevent the needle valve 19 from opening when the engine is stopped and to prevent fuel leakage.

The controller 50 controls the opening and closing of the first solenoid valve (switching valve) 18 and the second solenoid valve (pressure control valve) 25 as follows, so that the injection characteristics (fuel spray ) Is controlled to an optimum state according to the operating conditions.

This will be described with reference to FIG. 3. First, when the fuel is not injected, the controller 50 sets the first position.
Is closed, and the second electromagnetic valve 25 is opened. In this state, the supply of the high-pressure fuel to the internal passage 17 is shut off, while the pressure chamber 22 is in the discharge orifice 2.
4, the pressure chamber 22 has a substantially atmospheric pressure, the pressure in the internal passage 17 is low, and the needle valve 19
Is closed by the return spring 26.

In order to perform fuel injection, the controller 5
When the solenoid valve 18 opens the solenoid valve 18 (time t0), high-pressure fuel is introduced into the internal passage 17, but depending on the distance and volume between the solenoid valve 18, the pressure chamber 22, and the nozzle chamber 27, the pressure chamber 22 and the nozzle The pressure in the chamber 27 rises with a time delay.

Here, since the pressure chamber 22 has its inlet narrowed by the filling orifice 23 and the discharge orifice 24 is open, the pressure rise is much more gradual than that of the nozzle chamber 27 and the maximum. The value is also low. For this reason,
When the pressure in the nozzle chamber 27 exceeds the valve opening pressure determined by the set load of the return spring 26 at time t1, the needle valve 19 starts lifting. At this time, the main acting force acting on the needle valve 19 is the pressure of the nozzle chamber 27 and the spring force of the return spring 26. Once the needle valve 19 starts lifting, fuel is stored inside the needle valve seat. As a result, the effective pressure receiving area increases, so that the needle valve 19 opens to the maximum lift at once in response to the fuel pressure, and fuel injection starts.

Regarding the characteristics up to the opening of the valve, the behavior of the pressure in the nozzle chamber 27 and the behavior of the needle valve 19 in the initial stage of fuel injection are the same as those of the normal operation except for the method of generating the pressure wave supplied to the nozzle chamber 27. Same as jerk-type fuel injector,
Fuel spray with a long ignition delay can be obtained.

The fuel injection rate at the beginning of the injection does not reach its peak until the fuel pressure in the nozzle chamber 27 rises to the set pressure in the pressure accumulating chamber 9 (time t3). The time t3 is affected by the distance between the solenoid valve 18 and the nozzle chamber 27, the volume, the lift speed of the solenoid valve 18, and the like. For example, if the volume is increased, the initial injection rate can be suppressed. Become.

When the injection of fuel is stopped after a predetermined injection period, the controller 50 closes the solenoid valve 25. Then, since the discharge orifice 24 is closed, the pressure in the pressure chamber 22 increases, and after the time t4, the nozzle piston 21 pushes down the needle valve 19, and at the time t5, the needle valve 1
9 is seated, and the fuel injection ends.

In this case, the nozzle piston 21 is
The needle valve 19 starts to be driven in the valve closing direction while the pressure in the pressure chamber 22 is lower than the pressure in the nozzle chamber 27. During the movement of the needle valve 19 integrally with the nozzle piston 21, the pressure chamber 22 expands, so that the pressure does not become higher than the movement start pressure.

In this way, during and after the fuel injection, the characteristics are the same as those of the accumulator type fuel injection device.
That is, in this injection device, after the needle valve reaches the maximum lift, the injection pressure at that time can be freely adjusted according to the operating condition by setting the pressure of the pressure accumulation chamber 9. And the same fuel spray.

When the fuel injection is completed, the solenoid valve 18 is closed at time t6. Although there is high-pressure residual fuel in the internal passage 17, the needle valve sliding portion, the nozzle piston sliding portion, the solenoid valve 25
The pressure in the pressure chamber 22 and the nozzle chamber 27 decreases with time due to leakage from the nozzle chamber 27 and the like.
When the pressure becomes lower than a certain pressure, even if the solenoid valve 25 is opened and the pressure in the pressure chamber 22 is further reduced, the force for lifting the needle valve 19 against the return spring 26 does not work. Therefore, when the pressure has sufficiently decreased, the solenoid valve 25 is opened at time t7 to prepare for the next cycle.

Therefore, in this fuel injection device, the spray at the beginning of the injection becomes poor in ignition performance, that is, a fuel spray with a long ignition delay, as in the conventional jerk type fuel injection device. The fuel pressure in the accumulator 9 can be set to the optimum injection pressure according to the operating conditions, while ensuring the premixed combustion ratio and realizing the combustion with less smoke generation. With the same characteristics as the accumulator type fuel injection device, the combustion performance can be improved.

That is, according to the present invention, a fuel injection device having both the quality of the fuel spray obtained only by the jerk type fuel injection device and the degree of freedom of the injection pressure setting obtained only by the accumulator type fuel injection device is provided. Can be provided.

Although the solenoid valve 25 is opened at time t7, after the solenoid valve 25 is opened and closed for a short time after time t6, the solenoid valve 25 is opened again to prepare for the next injection. Good. For example, if the engine speed is high and the interval between injections is short, or if there is little fuel leakage from the needle valve 19 or the piston sliding portion, the solenoid valve 2 is not required until the next injection.
In some cases, the pressure in the pressure chamber 22 and the pressure in the nozzle chamber 27 may not drop sufficiently until the needle valve 19 does not lift even when the valve 5 is opened. In such a case, even if the pressure is high, the needle valve 1
By opening the solenoid valve 25 only for a very short time during which the lift 9 is not lifted, the pressure can be reduced even a little, and the rise of the next injection can be improved accordingly. The opening and closing of the solenoid valve 25 for a short time may be repeated a plurality of times.

By the way, the controller 50 operates the electromagnetic valve 18
And 25 are changed from the above-described first injection mode, whereby the fuel injection characteristics are switched to the same characteristics as a normal pressure-accumulation type fuel injection device, that is, the second injection mode described below, depending on operating conditions. be able to.

To explain this, in the second injection mode, the controller 50 holds the solenoid valve 18 in the fully open state and controls only the solenoid valve 25 to open and close according to the injection timing.

Since the electromagnetic valve 18 is always open, high-pressure fuel is always guided to the internal passage 17 and the nozzle chamber 7.
Here, when fuel injection is not performed, the solenoid valve 25 is closed, so that the pressure in the pressure chamber 22 becomes the same as that in the nozzle chamber 27, and the needle valve 19 is pushed by the nozzle piston 21 and closed.

When the fuel injection timing comes, the controller 50
Opens the solenoid valve 25. Then, the fuel in the pressure chamber 22 is leaked through the discharge orifice 24, and the pressure is reduced. From a certain point, the force for lifting the needle valve 19 becomes larger than the force for pushing the needle valve 19 in the valve closing direction, and the needle valve 19 is lifted. Fuel is injected.

When the predetermined injection period has elapsed, the solenoid valve 25 is closed. As a result, the pressure in the pressure chamber 22 starts to increase, and when the force by which the nozzle piston 21 pushes down the needle valve 19 in the valve closing direction exceeds, the needle valve 19 is seated, and the fuel injection ends.

The above-described injection mode is basically the same as that of a normal pressure-accumulation type fuel injection device, whereby a fuel spray having excellent ignitability can be obtained.

Therefore, when the operating characteristics of the solenoid valve 18 and the solenoid valve 25 are switched between the first injection mode and the second injection mode as described above depending on the operating conditions, the spray characteristics can be switched. For example, when the fuel injection is controlled by opening and closing the solenoid valve 25 while the solenoid valve 18 is kept open during low rotation, low load, or cold operation, a spray having good ignitability can be obtained. For example, when performing high load or low temperature premix combustion, the solenoid valve 18 is required.
By controlling the opening and closing of the solenoid valve 25 and the opening and closing of the solenoid valve 25, it is possible to further improve exhaust performance, fuel consumption performance, smoke emission, and the like.

The second embodiment will be described with reference to FIG.

This embodiment differs from the first embodiment only in that a spring 28 for urging the nozzle piston 21 in the lift direction of the needle valve 19 is provided.

Therefore, in the first injection mode,
At the time of fuel injection, that is, when the pressure in the pressure chamber 22 decreases,
The action force of the spring 28 pushing up the nozzle piston 21 substantially reduces the mass of the movable part that moves together with the needle valve 19, so that the needle valve 19 is quickly lifted.

For this reason, it is possible to obtain a spray with a longer ignition delay, and it is possible to improve the smoke reduction performance under a high load.

Next, a third embodiment is shown in FIG.

In this embodiment, as the switching valve, a valve that opens and closes using fuel pressure is provided instead of opening and closing the fuel passage 16 directly by the solenoid valve 18 as in the first embodiment.

A sliding valve 29 for opening and closing the fuel passage 16 and a piston 30 for pressing the sliding valve 29 in the valve closing direction are provided. A second charging orifice 32 is provided in a pressing chamber 31 in which the piston 30 slides. , And connected to the drain side via a second discharge orifice 33, and the second discharge orifice 33 is opened and closed by an electromagnetic valve 34.

In this case, when the solenoid valve 34 is closed, the pressure in the pressing chamber 31 and the pressure acting on the valve chamber 35 of the sliding valve 29 become equal, but the pressure receiving area of the piston 30 is reduced.
The sliding valve 29 is seated and closed by making it larger than the pressure receiving area 9.

When the solenoid valve 34 is opened from this state, high pressure leaks from the discharge orifice 33 and the pressure chamber 31
Since the high pressure is introduced through the filling orifice 32, the pressure in the pressing chamber 31 becomes lower than the pressure in the valve chamber 35, the sliding valve 29 is opened, and the high-pressure fuel flows through the internal passage 17.

When the solenoid valve 34 is closed, the discharge orifice 33 is closed, the pressure in the pressing chamber 31 is increased, the sliding valve 29 is closed by the piston 30, and the supply of fuel is shut off.

Therefore, in this embodiment, the fuel passage 16 is not directly opened and closed by the solenoid valve, but the solenoid valve 34 only controls the pressure of the pressing chamber 31 and the sliding valve 29 is Since the operation is performed using the controlled fuel pressure, the capacity of the solenoid valve can be much smaller than that of the direct drive system, and the drive circuit can be simplified and downsized.

The behavior of the sliding valve 29 can be freely changed by setting the area of the second filling orifice 32 and the discharging orifice 33 and the pressure receiving area of the piston 30. By matching the fuel pressure characteristics to be applied, the fuel injection rate can be optimized.

The injection mode can be switched between the first mode and the second mode, as in the first embodiment.

In each of the above embodiments, an electromagnetic valve is used as an actuator. Instead of this, for example, a piezo actuator using a piezoelectric element may be used. Further, the pressure of the pressure chamber 22 is controlled by the solenoid valve 2.
5. The control is performed by the balance of the passage area of the filling orifice 23 and the discharge orifice 24. However, for example, a three-way solenoid valve may be used to switch the pressure of the pressure chamber 22 between the accumulation chamber side and the drain side. Good. Furthermore, an on-off valve for opening and closing a passage between the pressure accumulating chamber 9 and the injector 14,
That is, the electromagnetic valve 18 and the like are housed in a part of the injector housing.
Or at the outlet of the accumulator 9.

The present invention is not limited to the above embodiment,
Obviously, various modifications can be made within the scope of the technical idea.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a fuel supply system according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the injector according to the first embodiment.

FIG. 3 is an explanatory diagram showing operating characteristics of a needle valve.

FIG. 4 is a schematic sectional view of an injector according to a second embodiment.

FIG. 5 is a schematic sectional view of an injector according to a third embodiment.

FIG. 6 is a schematic sectional view of a conventional injector.

FIG. 7 is an enlarged sectional view of a tip portion of a nozzle.

FIG. 8 is a diagram showing a fuel flow velocity distribution in an ideal nozzle injection hole.

FIG. 9 is a view taken along line AA of FIG. 7;

FIG. 10 is a view taken along the line BB in FIG. 9;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel supply pump 9 fuel accumulator 14 injector 16 fuel passage 17 internal passage 18 solenoid valve 19 needle valve 21 nozzle piston 22 pressure chamber 25 solenoid valve 26 return spring 50 controller

Continued on the front page F term (reference) 3G066 AA07 AB02 AC09 AD12 BA05 BA13 BA14 BA22 BA24 BA25 BA67 CA01S CB08U CB12 CC06T CC08T CC14 CC26 CC48 CC51 CC52 CC64T CC66 CC67 CC68U CC70 CD26 CE02 CE13 CE22 DA11 DA13 DA14 DB08 DC09 DC12 DC13 DC18

Claims (5)

[Claims] 1. A fuel accumulator for storing fuel pressurized by a fuel supply pump in a high pressure state, and a valve for opening and closing the high pressure fuel from the fuel accumulator according to the pressure of a pressure chamber controlled by a pressure control valve. A fuel injection device for a diesel engine, comprising: an injector that injects fuel through the fuel injector; and a switching valve that selectively communicates and shuts off a fuel passage that connects the injector and the fuel pressure accumulation chamber; and the pressure control valve and the switching valve. A controller for controlling the valve, the controller closing the switching valve before fuel injection, opening the pressure control valve to keep the pressure chamber at a low pressure, and opening the switching valve at a fuel injection start timing. The fuel injection is performed by closing the valve, and at the end of the injection, the pressure control valve is closed to increase the pressure in the pressure chamber to terminate the fuel injection, and thereafter, the switching valve is closed. Fuel injection device for diesel engines. 2. A fuel accumulator for storing fuel pressurized by a fuel supply pump in a high pressure state, and a valve for opening and closing the high pressure fuel from the fuel accumulator according to the pressure of the pressure chamber controlled by a pressure control valve. A fuel injection device for a diesel engine, comprising: an injector that injects fuel through the fuel injector; and a switching valve that selectively communicates and shuts off a fuel passage that connects the injector and the fuel pressure accumulation chamber; and the pressure control valve and the switching valve. A controller for controlling the control valve, the controller closes the switching valve before fuel injection, opens the pressure control valve to maintain the pressure chamber at a low pressure, and controls the switching valve at a fuel injection start timing. A first injection mode in which the valve is opened to inject fuel, the pressure control valve is closed at the end of the injection to raise the pressure in the pressure chamber to end the fuel injection, and then the switching valve is closed. While holding the switching valve open, the pressure control valve is opened at the fuel injection start timing to perform the fuel injection at a low pressure in the pressure chamber, and the pressure control valve is closed at the injection end timing to close the pressure control valve. A fuel injection device for a diesel engine, which can be switched to a second injection mode in which the pressure chamber is set to a high pressure and fuel injection is stopped. 3. The fuel injection device for a diesel engine according to claim 1, wherein the controller opens and closes the pressure control valve for a very short time after the end of fuel injection in the first injection mode. 4. A needle valve which lifts up and opens an injection hole when the injector receives high fuel pressure, a spring for urging the needle valve in a closing direction, a pressure chamber into which the fuel pressure is introduced, A piston that presses the needle valve in the opening direction in accordance with the pressure of the chamber, a spring that urges the piston in the direction opposite to the valve closing direction of the needle valve, and a drain chamber of the pressure chamber that opens and closes to adjust the pressure The fuel injection device for a diesel engine according to claim 1, further comprising a pressure control valve. 5. A sliding valve, wherein the switching valve lifts and opens when receiving a high fuel pressure, a pressing chamber to which the fuel pressure is guided, and the sliding valve according to the pressure of the pressing chamber. The fuel injection device for a diesel engine according to any one of claims 1 to 4, further comprising: a piston that presses the pressure in a valve closing direction; and a control valve that adjusts a pressure of the pressing chamber.