JP4216262B2 - Fuel injection system for diesel engine - Google Patents

Description

  The present invention introduces high-pressure fuel pressurized to a high pressure by a fuel injection pump into a fuel injection valve, and the pressure of the high-pressure fuel in the fuel injection valve exceeds the valve opening pressure of a needle valve provided in the fuel injection valve. The present invention relates to a diesel engine configured to open the hour valve and inject the high-pressure fuel into a combustion chamber of the engine from an injection hole provided in the fuel injection valve.

FIG. 9A is a system diagram showing a schematic configuration of a fuel injection device of a diesel engine. In the figure, 1 is a fuel injection pump, 5 is a fuel injection valve, and 14 is a poppet valve that opens and closes a supply / discharge oil passage 15. The high-pressure fuel in the plunger chamber 11 pressurized to a high pressure by the plunger 1 a of the fuel injection pump 1 closes the poppet valve 14 and the oil supply / discharge passage 15, pushes the discharge valve 2 and passes through the injection pipe 4. It is introduced into the fuel injection valve 5. 3 is an isobaric valve.
The high-pressure fuel stored in the fuel reservoir 53 of the fuel injection valve 5 is set by the opening pressure of the needle valve 51 provided on the fuel injection valve 5, that is, the set pressure of the needle valve spring 54. When the needle valve 51 is opened by the pressure of the high-pressure fuel exceeding the set valve opening pressure, the fuel is injected into the combustion chamber 30 of the engine from the injection hole 52 provided in the fuel injection valve 5.

  Patent Document 1 (Japanese Patent Laid-Open No. 5-71438) discloses a high pressure fuel supply by controlling a pressure in a back pressure chamber by providing a back pressure control valve on the low pressure side of a three-way solenoid valve provided in an injector. There has been proposed a fuel injection device for a diesel engine that can obtain an optimal injection mode for combustion that has a low injection rate in the early stage of injection and a high injection rate in the late stage of injection.

Japanese Patent Laid-Open No. 5-71438

  In a diesel engine, at a high load such as rated output (high output), the fuel injection pressure from the fuel injection valve 5 is set to a high pressure so that the smoke concentration is maintained at a good level (fuel consumption rate). Therefore, in the conventional engine shown in FIG. 9, the valve opening pressure of the needle valve 51 (that is, the set pressure of the needle valve spring 54) is increased to increase the injection pressure. Things have been done.

That is, FIG. 9B shows the lift of the needle valve 51 and the fuel injection mode in the conventional engine. In such a conventional engine, the injection pressure at the time of high load as shown by line A in FIG. When the injection mode to be increased is set, the injection mode at the time of low load indicated by the line B in FIG. 5 is constant because the valve opening pressure P0 of the needle valve 51 is constant from the low load to the high load. Thus, the initial injection rate becomes an excessive injection rate at the same level as that at the time of high load.
For this reason, in such a conventional engine, as an injection mode in which the injection pressure at the time of high load operation is increased, if the exhaust gas concentration is maintained well and the fuel consumption (fuel consumption rate) is reduced, the operation at the time of low load operation such as partial load There is a problem in that the initial injection rate becomes excessive, leading to an increase in NOx (nitrogen oxide).

  On the other hand, in the technique provided in Patent Document 1 (Japanese Patent Laid-Open No. 5-71438), the injection is performed so that the injection rate is low at the initial stage of injection even when high-pressure fuel is supplied and the injection rate is high at the late stage of injection. Only the means to control the mode is shown, and when the injection mode is set to increase the injection pressure at high load to maintain good flue gas concentration and reduce fuel consumption, the initial injection rate at low load is No means for solving the problem of excessively increasing NOx is shown.

  In view of the problems of the prior art, the present invention increases the injection pressure at the time of high load operation, reduces fuel consumption, maintains a good smoke concentration, and makes it possible to suppress NOx emission at low loads. An object of the present invention is to provide a fuel injection device for a diesel engine.

The present invention achieves such an object, in which high-pressure fuel pressurized to a high pressure by a fuel injection pump is introduced into a fuel injection valve, and the pressure of the high-pressure fuel in the fuel injection valve is provided in the fuel injection valve. In the diesel engine configured to open the needle valve when the valve opening pressure of the needle valve is exceeded and inject the high-pressure fuel into the combustion chamber of the engine from the injection hole provided in the fuel injection valve, A hydraulic cylinder device that changes the valve opening pressure by changing the pressing pressure to the valve seat of the needle valve, and a hydraulic oil passage provided to the hydraulic oil passage to the hydraulic cylinder device to change a passage area of the hydraulic oil passage a poppet valve mechanism for controlling the solenoid valve, the supply and discharge oil passage of the fuel injection pump is opened and closed in two stages fuel injection timing for varying the pressing pressure of the needle valve by the hydraulic cylinder device by the electric And a controller for setting the opening pressure to control the valve opening pressure by changing the opening degree of the valve in two stages smaller opening pressure than the shelf pressure formed by closing of the poppet valve mechanism It is characterized by that.

In this invention, specifically, the controller is configured to form a shelf pressure by two-stage closing of the poppet valve mechanism during low load operation .

In the present invention , the controller controls the valve opening pressure by changing the opening of the electromagnetic valve according to the change in the fuel injection amount so as to increase the valve opening pressure as the fuel injection amount of the engine increases. Configure as follows .

In the present invention, the controller sets the relationship between the fuel injection timing of the engine and the flue gas concentration, and the relationship between the fuel injection timing and the NOx (nitrogen oxide) emission amount. The optimal fuel injection timing at which the NOx emission amount is less than the allowable emission amount and the valve opening pressure becomes the optimum valve opening pressure corresponding to the optimum fuel injection timing. The valve opening pressure is controlled by changing the opening of the electromagnetic valve .

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According to the present invention, the hydraulic cylinder device that changes the valve opening pressure by changing the pressing pressure of the needle valve in the fuel injection valve, and the hydraulic pressure by changing the passage area of the hydraulic oil passage to the hydraulic cylinder device. An electromagnetic valve that changes the pressing pressure of the needle valve by the cylinder device is provided, and preferably calculated by the controller based on the set value of the fuel injection amount calculated based on the engine load and the engine speed and the opening of the electromagnetic valve The opening of the solenoid valve is controlled so that the valve opening pressure becomes the valve opening pressure corresponding to the set value of the fuel injection amount, and the valve opening pressure is increased as the fuel injection amount increases. Since the valve opening pressure is controlled by changing the opening of the solenoid valve according to the change of the fuel injection amount so as to increase, the valve opening pressure is increased during high load operation with a large amount of fuel injection, As an injection mode in which the injection pressure is increased and the injection period is shortened, operation with reduced fuel consumption and good smoke density is possible, and the valve opening pressure is shifted low during low load operation with a small fuel injection amount. Therefore, it is possible to perform an operation in which the initial injection rate is lowered to suppress the rise of combustion and NOx emission is suppressed.
Therefore, according to the present invention, the valve opening pressure is controlled by changing the opening of the solenoid valve in accordance with the change in the fuel injection amount, so that the valve opening pressure is raised during high load operation to maintain a good smoke concentration. A diesel engine having both the effects of reducing fuel consumption and reducing NOx emissions by lowering the valve opening pressure and lowering the initial injection rate during low-load operation can be obtained.
Further, according to the present invention, a poppet valve mechanism for controlling the fuel injection timing by opening and closing the supply / discharge oil passage of the fuel injection pump in two stages is provided, and the valve opening pressure is controlled by the controller in two stages of the poppet valve mechanism. The valve opening pressure is set to be smaller than the shelf pressure formed by the two-stage closing of the poppet valve mechanism when the engine is operated at a low load. Thus, the fuel injection can be performed in the injection mode in which the shelf pressure formed by the two-stage closing of the poppet valve mechanism is formed, the initial injection rate can be kept low, and the NOx emission suppressing effect is more remarkable. It becomes.

Further, according to the present invention, the hydraulic cylinder device that changes the valve opening pressure by changing the pressing pressure of the needle valve in the fuel injection valve, and the passage area of the hydraulic oil passage to the hydraulic cylinder device are changed, An electromagnetic valve for changing the pressing pressure of the needle valve by the hydraulic cylinder device, and preferably, by the controller, the smoke concentration is less than or equal to a preset allowable smoke concentration based on a detected value of the smoke concentration. And calculating the optimal fuel injection timing such that the NOx emission amount is equal to or less than the allowable NOx emission amount corresponding to the engine load or the engine speed, calculating the optimal valve opening pressure corresponding to the optimal fuel injection timing, and opening the valve Since the valve opening pressure is controlled by changing the opening of the electromagnetic valve so that the pressure becomes the optimum valve opening pressure,
In high-load operation, the valve opening pressure is increased to increase the injection pressure and the injection period is shortened, so that the smoke concentration is kept below the allowable smoke concentration and the valve opening pressure is shifted low during low-load operation. As a result, the initial injection rate can be lowered to suppress the rise of combustion, thereby suppressing NOx emission.
Therefore, according to the present invention, the valve opening pressure is controlled by changing the opening of the solenoid valve so that the optimum valve opening pressure corresponding to the optimum fuel injection timing calculated from the smoke concentration and the NOx emission amount is obtained. By doing this, a diesel engine that can be operated while suppressing the smoke concentration below the allowable smoke concentration and suppressing the NOx emission amount below the allowable NOx emission amount in the entire operation region is obtained.

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  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

FIG. 1 is a system diagram showing a schematic configuration of a fuel injection device for a diesel engine according to a first embodiment of the present invention.
In FIG. 1, 1 is a fuel injection pump, 5 is a fuel injection valve, 14 is a poppet valve that opens and closes the supply / discharge oil passage 15, and the inside of the plunger chamber 11 is pressurized to a high pressure by the plunger 1 a of the fuel injection pump 1. When the poppet valve 14 closes the supply / discharge oil passage 15, the high pressure fuel pushes the discharge valve 2 and is introduced into the fuel reservoir 53 of the fuel injection valve 5 through the injection pipe 4. 52 is a nozzle hole provided in the fuel injection valve 5, and 51 is a needle valve that opens and closes between the fuel reservoir 53 and the nozzle hole 52. 3 is an isobaric valve.
The above configuration is the same as that of the conventional fuel injection device shown in FIG.

6 is a hydraulic cylinder, 8 is a hydraulic source that supplies pressurized hydraulic oil, and 9 is a hydraulic oil pipe that connects the hydraulic source 8 and the hydraulic cylinder. 7 is an electromagnetic valve provided in the hydraulic oil pipe 9, whose opening degree is controlled by a control signal from a controller 10 described later, and the passage area of the hydraulic oil passage including the hydraulic oil pipe 9 is changed.
The valve opening pressure of the needle valve 51 is constituted by the resultant force of the hydraulic pressure in the hydraulic cylinder 6 and the set pressure of the needle valve spring 54, and the pressure of the high pressure fuel in the fuel reservoir 53 is the needle valve 51. When the valve opening pressure is exceeded, the needle valve 51 is lifted and opened by the pressure of the high-pressure fuel, and injected from the nozzle hole 52 into the combustion chamber 30 of the engine.

Reference numeral 12 denotes a rotational speed detector that detects the rotational speed of the engine (engine rotational speed), 11 denotes a load detector that detects the load of the engine (engine load), and 13 denotes the smoke concentration in the exhaust gas discharged from the engine. It is a smoke sensor to detect.
Reference numeral 10 denotes a controller. The detected value of the engine speed from the engine speed detector 12, the detected value of the engine load from the load detector 11, and the detected value of the smoke concentration from the smoke sensor 13 are the controller 10's. The controller 10 controls the opening degree of the electromagnetic valve 7 according to the procedure described later.

Next, based on the control block diagram of FIG.2 and FIG.3, operation | movement of this 1st Example is demonstrated.
FIG. 2 is a control block diagram (part 1) in the first embodiment (partly the second embodiment), and FIG. 3 is a control block diagram (part 2) in the first embodiment (partly the second embodiment). ).
In FIG. 2, the detected value of the engine speed from the engine speed detector 12 and the detected value of the engine load from the load detector 11 are input to the injection amount calculation unit 101 of the controller 10. Reference numeral 102 denotes an injection amount setting unit in which a fuel injection amount for the engine speed and / or engine load is set.
In the injection amount calculation unit 101, a fuel injection amount corresponding to the detected value of the engine speed and / or the detected value of the engine load is extracted from the injection amount setting unit 102 and input to the valve opening pressure calculation unit 103. .

A valve opening pressure setting unit 104 is set so that the valve opening pressure increases as the fuel injection amount increases, as shown in FIG.
In the valve opening pressure calculation unit 103, the valve opening pressure corresponding to the extracted value of the fuel injection amount from the injection amount calculation unit 101 is extracted from the valve opening pressure setting unit 104 and input to the electromagnetic valve control unit 105. . The electromagnetic valve control unit 105 calculates the opening degree of the electromagnetic valve 7 so as to be the extracted value of the valve opening pressure, and adjusts the electromagnetic valve 7 to the calculated opening degree. Accordingly, the operating hydraulic pressure of the hydraulic cylinder 6 is adjusted to the operating hydraulic pressure corresponding to the extracted value of the valve opening pressure by the electromagnetic valve 7, and the valve opening pressure of the needle valve 51 (see FIG. 1) is extracted from the valve opening pressure extraction. Set to a value.

According to the first embodiment, the hydraulic cylinder 6 that changes the valve opening pressure by changing the pressing pressure of the needle valve 51 in the fuel injection valve 5 and the passage area of the hydraulic oil passage to the hydraulic cylinder 6 are changed. Thus, an electromagnetic valve 7 for changing the pressing pressure of the needle valve 51 by the hydraulic cylinder 6 is provided, and the set value of the fuel injection amount calculated by the controller 10 based on the engine load and / or the engine speed and the electromagnetic The valve opening pressure calculated based on the opening degree of the valve 7 is compared, and the opening degree of the electromagnetic valve 7 is controlled so that the valve opening pressure becomes the valve opening pressure corresponding to the set value of the fuel injection amount. Since the valve opening pressure is controlled by changing the opening of the electromagnetic valve 7 according to the change in the fuel injection amount so as to increase the valve opening pressure in accordance with the increase in the injection amount, high load operation with a large fuel injection amount is achieved. Sometimes As an injection mode in which the valve opening pressure is increased, the injection pressure is increased, and the injection period is shortened, it is possible to maintain a good smoke concentration and reduce fuel consumption, and at the time of low load operation with a small fuel injection amount An operation that shifts the valve opening pressure low, lowers the initial injection rate, suppresses the rise of combustion, and suppresses NOx emission becomes possible.
Therefore, according to the first embodiment, the valve opening pressure is controlled by changing the opening degree of the electromagnetic valve 7 according to the change in the fuel injection amount, thereby increasing the valve opening pressure during the high load operation, thereby reducing the smoke concentration. It is possible to obtain a diesel engine that has both effects of being able to maintain good conditions and reduce fuel consumption, and to reduce NOx emission by lowering the valve opening pressure and lowering the initial injection rate during low load operation.

Next, in FIG. 3, the detected value of the engine speed from the rotational speed detector 12, the detected value of the engine load from the load detector 11, and the detected value of the smoke concentration from the smoke sensor 13 are the controller. 10 injection timing calculation units 106.
Reference numeral 108 denotes a smoke / injection timing setting unit. As shown in FIG. 4A, the relationship between the allowable smoke concentration and the injection timing is set so that the smoke concentration decreases as the injection timing is advanced. Reference numeral 107 denotes a NOx / injection timing setting unit for setting an allowable NOx emission amount at the fuel injection timing corresponding to the engine load or the engine speed, and as shown in FIG. Is set to increase.

In the injection timing calculation unit 106, the smoke concentration is preset in the smoke / injection timing setting unit 108 based on the detected value of the engine speed and / or the detected value of the engine load and the detected value of the smoke concentration. Optimal fuel injection so that the NOx emission amount is less than the allowable NOx emission amount corresponding to the engine speed and / or engine load set in the NOx / injection timing setting unit 107. Timing is calculated and input to the valve opening pressure calculation unit 110.
Reference numeral 111 denotes a valve opening pressure setting unit in which a relationship between the optimum fuel injection timing and the valve opening pressure is set, and during the high load operation, the smoke concentration is set in the smoke / injection timing setting unit 108. A high valve opening pressure corresponding to the fuel injection timing regulated to be below is set, and the NOx emission amount becomes equal to or less than the allowable NOx emission amount set in the NOx / injection timing setting unit 107 during low load operation. Thus, the valve opening pressure shifted to a value lower than that during the high load operation corresponding to the regulated fuel injection timing is set.

The valve opening pressure calculation unit 110 calculates a valve opening pressure during high load operation and a valve opening pressure during low load operation corresponding to the optimum fuel injection timing from the injection timing calculation unit 106, and an electromagnetic valve control unit 112.
The electromagnetic valve control unit 112 calculates the opening degree of the electromagnetic valve 7 so that the calculated value of the valve opening pressure is obtained, and adjusts the electromagnetic valve 7 to the calculated opening degree. Accordingly, the operating hydraulic pressure of the hydraulic cylinder 6 is adjusted to the operating hydraulic pressure corresponding to the extracted value of the valve opening pressure by the electromagnetic valve 7, and the valve opening pressure of the needle valve 51 (see FIG. 1) is calculated as the valve opening pressure. Set to a value.

Therefore, according to the control system of FIG. 3 in the first embodiment,
Based on the detected value of the smoke concentration, the smoke concentration is not more than a preset allowable smoke concentration and the NOx emission amount is not more than the allowable NOx emission amount corresponding to the engine load or the engine speed. The optimum fuel injection timing is calculated, the optimum valve opening pressure corresponding to the optimum fuel injection timing is calculated, and the opening degree of the electromagnetic valve 7 is changed so that the valve opening pressure becomes the optimum valve opening pressure. Since it was configured to control the valve opening pressure,
In the injection mode in which the valve opening pressure is increased during high load operation to increase the injection pressure and the injection period is shortened, the smoke concentration is kept below the permissible smoke concentration, and the valve opening pressure is shifted low during low load operation. As a result, the initial injection rate can be lowered to suppress the rise of combustion, thereby suppressing NOx emission.
Thus, by controlling the valve opening pressure by changing the opening of the electromagnetic valve 7 so as to obtain the optimum valve opening pressure corresponding to the optimum fuel injection timing calculated from the smoke concentration and the NOx emission amount. Thus, a diesel engine can be obtained that can be operated while suppressing the smoke concentration below the allowable smoke concentration and suppressing the NOx emission below the allowable NOx emission in the entire operation range.

FIG. 5 (B) shows the control system set from the relationship between the fuel injection amount and the valve opening pressure in FIG. 2 (FIG. 5 (A)), the smoke concentration and NOx emission amount and the valve opening pressure in FIG. The needle valve lift and the fuel injection mode combined with the control system set from the relationship are shown.
In FIG. 5B, A is a fuel injection mode at a high valve opening pressure P2 set by the fuel injection amount and smoke concentration during a high load operation, and B is a fuel injection mode at a low load operation. The fuel injection mode is set at the valve opening pressure P1 shifted to a value lower than the valve opening pressure P2 set by the amount and the NOx discharge amount.

FIG. 6 is a view corresponding to FIG. 1 showing a second embodiment of the present invention, and FIG. 7 is a configuration diagram of a poppet valve mechanism in the second embodiment.
In this second embodiment, instead of the poppet valve mechanism 14 in the first embodiment of FIG. 1, a poppet valve mechanism 140 capable of two-stage opening and closing as shown in FIG. 7 is installed.
That is, in FIG. 7, the supply / discharge oil passage 15 connected to the plunger chamber 11 of the fuel injection pump 1 is branched into two oil discharge passages 144 and 145 and connected to the fuel tank 16, and each oil discharge passage is also connected. 144 and 145 are provided with solenoid type on-off valves 141 and 142 that are opened and closed by the controller 10 to open and close the oil drain passages 144 and 145, respectively. Reference numeral 143 is a pressure equalizing device, and 5 is a fuel injection valve.

In the second embodiment, when both the on-off valves 141 and 142 are opened, the fuel in the plunger chamber 11 of the fuel injection pump 1 is discharged from the two oil discharge passages 144 and 145 to the fuel tank 16 to perform fuel injection. I can't.
When both of the on-off valves 141 and 142 are closed, the two oil discharge passages 144 and 145 are closed to increase the pressure in the plunger chamber 11, and when the valve opening pressure is reached, fuel injection is started. The fuel injection mode at this time is the injection mode shown in FIG. 8B corresponding to the high load operation.

When either one of the on-off valves 141 and 142 is closed, the fuel injection mode at this time becomes the injection mode shown in B of FIG. 8 (B) corresponding to the low load operation, and the shelf pressure B1 is set at the rise of the injection. By forming the valve opening pressure smaller than the shelf pressure B1, shelf pressure injection with a slow rise in injection becomes possible.
Therefore, according to the second embodiment, the poppet valve mechanism 14 that controls the fuel injection timing by opening and closing the two oil discharge passages 144 and 145 connected to the supply / discharge oil passage 15 of the fuel injection pump 1 in two stages. And the controller 10 sets the valve opening pressure to a valve opening pressure smaller than the shelf pressure B1 formed by closing one of the on-off valves 141 and 142 of the poppet valve mechanism 14. During low load operation, fuel injection can be performed in the injection mode in which the shelf pressure B1 formed by the two-stage closing of the poppet valve mechanism 14 is formed, and the initial injection rate is kept low and NOx is discharged. The suppression effect becomes more prominent.
Other configurations and operational effects are the same as those of the first embodiment shown in FIG. 1, and the same members or elements are denoted by the same reference numerals.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel injection of the diesel engine which can raise the injection pressure at the time of high load driving | operation, can reduce fuel consumption, can hold | maintain a flue gas density | concentration favorably, and can suppress the discharge | emission amount of NOx at the time of low load. Equipment can be provided.

1 is a system diagram showing a schematic configuration of a fuel injection device for a diesel engine according to a first embodiment of the present invention. It is the control block diagram (the 1) in the said 1st Example (a part is 2nd Example). It is the control block diagram (the 2) in the said 1st Example (a part is 2nd Example). (A), (B) is a relationship diagram of the injection timing in the said 1st, 2nd Example, flue gas density | concentration, and NOx discharge | emission amount. (A), (B) is a valve-opening pressure and injection pressure diagram in the said 1st Example. FIG. 3 is a view corresponding to FIG. 1 showing a second embodiment of the present invention. It is a block diagram of the poppet valve mechanism in the said 2nd Example. (A), (B) is a valve-opening pressure and injection pressure diagram in the said 2nd Example. (A) is a system diagram which shows schematic structure of the fuel injection apparatus of the conventional diesel engine, (B) is an injection pressure diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel injection pump 1a Plunger 2 Discharge valve 3 Isobaric valve 4 Injection pipe 5 Fuel injection valve 6 Hydraulic cylinder 7 Electromagnetic valve 10 Controller 11 Load detector 12 Revolution detector 13 Smoke sensor 14, 140 Poppet valve 15 Supply / drain passage 30 Combustion chamber 51 Needle valve 52 Injection hole

Claims (4)

When high pressure fuel pressurized to high pressure by a fuel injection pump is introduced into the fuel injection valve, the pressure of the high pressure fuel in the fuel injection valve exceeds the valve opening pressure of a needle valve provided in the fuel injection valve. In a diesel engine configured to inject the high-pressure fuel into a combustion chamber of an engine through a nozzle hole provided in the fuel injection valve when a needle valve is opened,
A hydraulic cylinder device that changes the valve opening pressure by changing the pressing pressure of the needle valve to the valve seat;
An electromagnetic valve that is provided in a hydraulic oil passage to the hydraulic cylinder device and changes a pressing pressure of the needle valve by the hydraulic cylinder device by changing a passage area of the hydraulic oil passage;
A poppet valve mechanism for controlling the fuel injection timing by opening and closing the supply / discharge oil passage of the fuel injection pump in two stages;
A controller for controlling the valve opening pressure by changing the opening of the electromagnetic valve and setting the valve opening pressure to a valve opening pressure smaller than a shelf pressure formed by two-stage closing of the poppet valve mechanism; fuel injection device for a diesel engine characterized by comprising. 2. The fuel injection device for a diesel engine according to claim 1 , wherein the controller forms a shelf pressure by two-stage closing of the poppet valve mechanism during low load operation . The controller controls the valve opening pressure by changing the opening of the electromagnetic valve according to the change in the fuel injection amount so as to increase the valve opening pressure as the fuel injection amount of the engine increases. The diesel engine fuel injection device according to claim 1 . The controller sets the relationship between the fuel injection timing of the engine and the flue gas concentration, and the relationship between the fuel injection timing and the NOx (nitrogen oxide) emission amount, and the flue gas concentration falls below an allowable concentration. And the opening degree of the solenoid valve is calculated so that the optimal fuel injection timing at which the NOx emission amount is less than or equal to the allowable emission amount and the valve opening pressure becomes the optimal valve opening pressure corresponding to the optimal fuel injection timing. 2. The fuel injection device for a diesel engine according to claim 1, wherein the valve opening pressure is controlled by changing the pressure .

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