JP2008208814A - Fuel injection control method of unit injector and control device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control method of a unit injector and a control device therefor which close a valve by rapidly performing the lowering of pressure from a high-pressure fuel injection period to the end of injection, thereby improving interruption sharpness of the injection. <P>SOLUTION: At the time of completion of fuel injection, a second valve 7 is opened first, and a needle-control piston 8 and a high-pressure fuel passage 11 are communicated with each other. Then a needle valve 5 is closed by thrust of the needle-control piston 8 and an energizing force of a spring 9. Then a first valve 6 is opened, and the plunger-discharge fuel is drained into a spill S. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel injection control method for a unit injector in which a fuel injection device and a fuel injection nozzle are integrated, and to a control device therefor, and particularly to an improvement in control of a needle valve of a nozzle.

As shown in FIG. 1, the unit injector 1 includes a plunger 2 that pressurizes and discharges fuel, and a fuel injection nozzle 3. The plunger 2 is driven by a cam C. The fuel injection amount and injection timing of the unit injector 1 are controlled by the control means 50.
In FIG. 1, an arrow F indicates fuel supply from a feed pump (not shown), and an arrow S indicates fuel return (spill).

With reference to FIGS. 2-4, the outline | summary of a structure in the conventional unit injector and its effect | action are demonstrated.
2 to 4, the nozzle 3 is screwed to the tip of the injector 1.
A needle valve 5 is configured inside the nozzle body 31. The needle valve 5 has a needle 32, and the needle 32 is slidably inserted into the nozzle body 31. The distal end side (the lower side in FIGS. 2 to 4) of the sliding portion of the needle 32 is configured to have a small diameter, and a needle chamber 33 is formed between the nozzle body 31 and the needle 32. And the front-end | tip part of the needle 32 is seated on the sheet | seat part of the nozzle main body 31, and it is comprised so that the fuel channel to the nozzle 34 may be interrupted | blocked.

A needle closing spring (hereinafter referred to as a spring) 9 is provided on the upper portion of the needle valve 5. The spring 9 urges the needle 32 in the direction of closing the needle valve 5 (downward in FIGS. 2 to 4).
A needle control piston 8 is also provided above the needle valve 5, and the needle 32 is biased in the closing direction by the hydraulic pressure from the needle control piston 8 in addition to the spring 9.

  Furthermore, a first valve (spill valve) 6 that operates with an electromagnetic coil L1 and a second valve (needle control valve) 7 that operates with an electromagnetic coil L2 are provided above the nozzle 3. A plunger 2 that is driven by a cam C (see FIG. 1) is provided above the spill valve 6 and the needle control valve 7.

Further, a passage 11 through which high-pressure fuel discharged from the discharge port 2a of the plunger flows is drilled to the needle chamber 33 of the nozzle.
From the high-pressure fuel passage 11, a passage 11A communicating with the spill valve 6 and a passage 11B communicating with the needle control valve 7 are branched.

The spill valve 6 is opened when the electromagnetic coil L1 is not energized, and communicates with the spill S from the high-pressure fuel passage 11. On the other hand, when the electromagnetic coil L1 is energized, the valve is closed to block the flow path to the spill S.
The needle control valve 7 is located closer to the nozzle 3 than the spill valve 6 (downward in FIGS. 2 to 4). When the electromagnetic coil L2 is not energized, the valve is opened and communicates from the high pressure fuel passage 11 to the needle control piston 8. On the other hand, when the electromagnetic coil L2 is energized, the valve is closed, the supply of high-pressure fuel from the high-pressure fuel passage 11 is shut off, and the needle control valve 7 communicates with the spill S.

  The diameter of the needle control piston 8 is configured to be the same as the diameter of the needle 32, and when the needle control valve 7 is opened, the pressing force by the needle control piston 8 (the pressing force downward in FIGS. 2 to 4). And the pressing force by the fuel pressure of the needle 32 (the pressing force upward in FIGS. 2 to 4) is balanced.

Next, the control by the control means 50 is demonstrated about each process in the fuel injection of the injector 1. FIG.
The spill valve 6 and the needle control valve 7 are opened during the fuel charge (plunger up stroke) and prestroke (initial stage of the plunger down stroke) period shown in FIG. Therefore, the fuel discharged from the plunger 2 flows out to the spill S through the spill valve 6, and the high-pressure fuel passage 11 has a low pressure.

In the pressure accumulation period shown in FIG. 3, the spill valve 6 is closed. Therefore, the high pressure fuel passage 11 is accumulated in a high pressure state by the fuel discharged from the plunger 2. At that time, the needle chamber 33 becomes high pressure, but since the needle control valve 7 is opened, a pressing force from the needle control piston 8 (downward pressing force in FIG. 3) is generated.
As described above, the pressing force from the needle control piston 8 balances with the pressing force of the needle chamber 33 (upward pressing force in FIG. 3). Therefore, the needle 32 is closed by the urging force of the spring 9 (downward force in FIG. 3).

In the fuel injection period shown in FIG. 4, the needle control valve 7 is closed.
When the needle control valve 7 is closed, the fuel pressure applied to the needle control piston 8 during the pressure accumulation period of FIG. Therefore, the force by the high pressure fuel in the needle chamber 33 applied to the lower surface of the needle 32 (upward force in FIG. 4) overcomes the elastic repulsion force (downward force in FIG. 4) of the spring 9, and the needle valve 5 is 4), the valve is opened and fuel injection is performed.

When the fuel injection period ends, the spill valve 6 and the needle control valve 7 are opened, and the state shown in FIG. 2 is restored.
Since the spill valve 6 communicates with the spill S side, the pressure of the high-pressure fuel passage 11 decreases and the force applied to the lower surface of the needle 32 in the needle chamber 33 also decreases. Then, the valve is closed by a downward force). Thereby, fuel injection is complete | finished.

As described above, the fuel injection end control in the conventional fuel injection control is performed by lowering the pressure of the high-pressure fuel passage 11 by opening the spill valve 6 and the needle control valve 7.
However, in this control, the pressure in the needle chamber 33 is reduced by opening the spill valve 6, and then the needle 33 is closed (by moving downward in FIGS. 2 to 4) by the biasing force of the spring 9. As a result, the pressure characteristic curve at the end of injection changes slowly, resulting in a so-called “bad” state.

That is, as indicated by the region PA in the characteristic line of the injection pressure shown in FIG. 7, the spill valve (SV) 6 and the needle control valve (NCV) 7 are opened (reference S on the horizontal axis in FIG. 7), and the injection pressure ( The vertical axis in FIG. 7 is gradually lowered, and the needle valve 5 is closed. Therefore, while the needle valve 5 is closed (region indicated by the symbol A), combustion is deteriorated and exhaust performance is deteriorated due to spray failure due to low injection pressure.
The conventional unit injector cannot improve such combustion deterioration and exhaust performance deterioration.

In addition, the technique which controls a nozzle needle valve and a spill valve is disclosed as a related well-known technique (for example, refer patent document 1).
However, such a conventional technique (Patent Document 1) cannot solve the above-described problems.
JP-A-6-299927

  The present invention has been proposed in view of the above-described problems of the prior art. In the unit injector, the pressure drop at the end of injection is rapidly performed to rapidly close the needle valve, thereby improving the spraying. It is an object of the present invention to provide a fuel injection control method and a control device therefor.

  The fuel injection control method for a unit injector according to the present invention comprises a plunger (2) that pressurizes and discharges fuel, and a needle valve (5) that is biased by a spring (9) by the discharged high-pressure fuel to open the fuel injection. In the fuel injection control method of a unit injector (1) integrally configured with a nozzle (3) to be performed, the unit injector (1) is connected to the needle valve (5) from a discharge port (2a) of a plunger. (11) is formed, the spill passage (11A) branched from the high-pressure fuel passage (11) and the first valve (spill valve 6) is interposed, and the needle valve (5) is closed by fuel oil pressure. A needle control piston (8) biasing in the direction and a second valve (needle control valve) communicating with the needle control piston (8). 7), and the second valve (7) communicates with the high-pressure fuel passage (11) when the valve is opened and to the spill (S) side when the valve is closed. In a period in which fuel is not injected, the first valve (6) and the second valve (7) are opened, and the fuel discharged from the plunger (2) is spilled (S In the fuel injection period, the first valve (6) is closed and the fuel discharged from the plunger (2) is sent to the needle valve (5). Subsequently, the second valve (7) Is closed to release the pressure of the needle control piston (8) to the spill (S), so that the needle valve (5) is opened with the discharged fuel pressure to perform fuel injection. 2 valve (7) is opened, the needle control piston (8) and the high-pressure fuel passage (11) are communicated, and the needle The needle valve (5) is closed by the pressing force of the front piston (8) and the urging force of the spring (9), and then the first valve (6) is opened to turn the plunger discharge fuel into the spill (S). It is made to flow out (Claim 1).

  A fuel injection control device for a unit injector according to the present invention opens a needle (5) energized by a spring (9) by a plunger (2) that pressurizes and discharges fuel, and performs fuel injection by opening the needle valve (5). In the fuel injection control means of the unit injector (1) integrally configured with the nozzle (3) to be performed, a high-pressure fuel passage (11) communicating with the needle valve (5) from the discharge port (2a) of the plunger is formed. A spill passage (11A) branched from the high-pressure fuel passage (11) and provided with a first valve (spill valve 6), and a needle control for urging the needle valve (5) in the valve closing direction by fuel oil pressure A piston (8), a second valve (needle control valve 7) communicating with the needle control piston (8), and a control means (50); The second valve (7) communicates with the high-pressure fuel passage (11) when the valve is opened, and communicates with the spill (S) side when the valve is closed. The control means (50) opens the first valve (6) and the second valve (7) during a period when fuel is not injected, and the fuel discharged from the plunger (2). Is discharged to the spill (S), and during the fuel injection period, the first valve (6) is closed and the fuel discharged from the plunger (2) is sent to the needle valve (5). Then, the second valve (7) is closed to release the pressure of the needle control piston (8) to the spill (S), so that the needle valve (5) is opened at the discharged fuel pressure and fuel injection is performed. When the fuel injection is finished, the second valve (7) is opened and the needle control piston (8) The pressure fuel passage (11) communicates, the needle valve (5) is closed by the pressing force of the needle control piston (8) and the urging force of the spring (9), and then the first valve (6) is opened. The valve is configured to execute control to flow the plunger discharge fuel to the spill (S) (Claim 2).

The present invention is configured as described above, and the control action at the end of the fuel injection period in the unit injector (1) is that the needle control valve (7) is opened and the spill valve (6) is subsequently opened. Performed in two steps with the valve.
At the end of the fuel injection period, first, the needle control valve (7) is opened, and the needle control piston (8) is connected to the high pressure fuel passage (11) from the low pressure state opened to the spill (S). Thus, since the pressing force of the piston (8) and the urging force of the spring (9) act on the needle valve (5), the needle valve (5) closes quickly even if the inside of the needle chamber (33) remains in a high pressure state.
Subsequently, the spill valve (6) is opened, and the pressures in the high-pressure fuel passage (11) and the needle chamber (33) are released to the spill (S) side to reduce the pressure.

Accordingly, at the end of fuel injection, even if the inside of the needle chamber (33) is in a high pressure state, the needle valve (5) can be quickly closed, so that it continues to open to a low pressure state as in the prior art. Disappears. Therefore, according to the present invention, there is no deterioration of the spray state, and the exhaust performance can be improved.
In addition, since “cut” at the end of fuel injection is good, it is possible to easily and accurately perform injection control in short-term injection such as pilot injection and post-injection or multistage injection combining them.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
The illustrated embodiment relates to control of a process in which injection is terminated from a fuel injection state by the control means 50 in the unit injector 1. The process will be described with reference to the flowchart shown in FIG. 5, taking the unit injector 1 described in FIGS. 2 to 4 as an example.

  In the fuel injection stroke shown in FIG. 4, both the spill valve 6 and the needle control valve 7 are closed. Therefore, the high pressure fuel discharged from the plunger 2 does not escape to the spill S side, but reaches the needle chamber 33 of the nozzle from the high pressure fuel passage 11, and the needle valve 5 causes the spring 9 to move by the pressure of the high pressure fuel. In FIG. 4, the urging force is overcome and the valve moves upward to open the valve, and fuel is injected from the nozzle 34.

In step S1 of FIG. 5, it is determined whether or not the injection amount or the injection period has reached a predetermined value. If the injection amount or the injection period has reached a predetermined value (Yes in step S1), valve opening control of the needle control valve (NCV) 7 is performed in step S2.
By opening the needle control valve (NCV) 7 (step S2), the pressure to the needle control piston 8 is released from the spill S as shown in FIG. The state changes to the state of communication with the fuel passage 11 (state of FIG. 6).

Therefore, the pressure of the high-pressure fuel (the discharge pressure of the plunger 2) acts from the high-pressure fuel passage 11 through the passage 11B in the region above the needle control piston 8 in FIG. The pressure of the high-pressure fuel (the discharge pressure of the plunger 2) acts together with the urging force of the spring 9 so as to push down the piston 8 in FIG.
As a result of the pressure of the high-pressure fuel (the discharge pressure of the plunger 2) and the biasing force of the spring 9 pressing the piston 8 downward, the needle 32 is pushed down and the needle valve 5 is closed. Thereby, fuel injection is complete | finished.
Here, since the pressure of the high-pressure fuel (the discharge pressure of the plunger 2) and the biasing force of the spring 9 press the piston 8 downward, the needle 32 is quickly pushed down and is seated, and the needle valve 5 is extremely closed. Done quickly.

Subsequently, the process proceeds to step S3, and after a predetermined period (time), the spill valve (SV) 6 is controlled to open, the high pressure fuel passage 11 is opened to the spill S, and the pressure from the high pressure fuel passage 11 to the needle chamber 33 is reduced. .
Thus, the fuel injection end process ends.
After that, the plunger 2 changes from the discharge stroke to the charge stroke, starts to rise, returns to the state of FIG. 2, and repeats the cycle described in FIG.

The completion of the fuel injection described in step S2 of FIG. 5 and FIG. 6 is preceded by the quick opening of the needle valve 5 by the opening of the needle control valve 7, and then the spill valve 6 is opened. The pressure in the high-pressure fuel passage 11 is reduced.
Therefore, regarding the end of fuel injection in the prior art, the injection in the low pressure state as described with respect to the region A in FIG. 7 is eliminated, and the so-called “good cutting” fuel injection can be ended.

  It should be noted that the illustrated embodiment is merely an example, and is not a description to limit the technical scope of the present invention.

The figure explaining the structure of a unit injector. Explanatory drawing which shows the prestroke state of a unit injector. Explanatory drawing which shows the pressure accumulation state of a unit injector. Explanatory drawing which shows the fuel-injection state of a unit injector. The flowchart which shows the fuel injection end control of the unit injector of this invention. Explanatory drawing which shows the state which the fuel injection in this invention complete | finished. The characteristic view which shows the characteristic of the injection pressure (needle chamber pressure) of the conventional nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Injector 2 ... Plunger 3 ... Nozzle 5 ... Needle valve 6 ... Spill valve 7 ... Needle control valve 8 ... Needle control piston 9 ... Spring 11, 11A, 11B ... Fuel passage 32 ... Needle 33 ... Needle chamber

Claims (2)

  In a fuel injection control method for a unit injector, in which a plunger that pressurizes and discharges fuel and a nozzle that opens a needle valve biased by a spring by the discharged high-pressure fuel and performs fuel injection are integrated, the unit injector includes: A high-pressure fuel passage communicating from the discharge port of the plunger to the needle valve is formed, a spill passage branched from the high-pressure fuel passage and a first valve interposed therein, and the needle valve in the valve closing direction by fuel hydraulic pressure An energizing needle control piston and a second valve communicating with the needle control piston are provided. When the second valve is opened, the second valve communicates with the high-pressure fuel passage and is closed. When the fuel is not injected, the first valve and the second valve are opened, and the spill side is configured to communicate with the spill side. The fuel discharged from the ranger is allowed to flow out into the spill, and during the fuel injection period, the first valve is closed and the fuel discharged from the plunger is sent to the needle valve, and then the second valve is closed to control the needle. The pressure of the piston is released to the spill, so that the needle valve is opened at the discharge fuel pressure and fuel injection is performed. At the end of the fuel injection, the second valve is opened and the needle control piston, the high-pressure fuel passage, The unit injector is characterized in that the needle valve is closed by the pressing force of the needle control piston and the biasing force of the spring, and then the first valve is opened to allow the plunger discharge fuel to flow out to the spill. Fuel injection control method.   In a fuel injection control means of a unit injector, in which a plunger that pressurizes and discharges fuel and a nozzle that opens a needle valve energized by a spring by the discharged high-pressure fuel and injects fuel are integrated, a discharge port of the plunger A high-pressure fuel passage communicating with the needle valve is formed, a spill passage branched from the high-pressure fuel passage and a first valve interposed therein, and a needle for biasing the needle valve in the valve closing direction by fuel hydraulic pressure A control piston, a second valve communicating with the needle control piston, and a control means are provided. The second valve communicates with the high-pressure fuel passage when the valve is opened and is closed. The control means is configured to communicate with the spill side, and the control means opens the first valve and the second valve during a period when fuel is not injected. Then, control is performed to cause the fuel discharged from the plunger to flow out to the spill. During the fuel injection period, the first valve is closed, the fuel discharged from the plunger is sent to the needle valve, and then the second valve is closed. The pressure of the needle control piston is released to the spill and the control is performed to open the needle valve with the discharged fuel pressure and perform fuel injection. At the end of fuel injection, the second valve is opened. The needle control piston communicates with the high-pressure fuel passage, the needle valve is closed by the pressing force of the needle control piston and the urging force of the spring, and then the first valve is opened and the plunger discharge fuel flows out to the spill. A fuel injection control device for a unit injector, characterized in that the control is executed.

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