JPH05272424A - Fuel injector for diesel engine - Google Patents

Abstract

PURPOSE:To satisfy various characteristics and stably obtain a high injection pressure by providing a pressure intensifying piston for pressurizing a needle valve under injection pressure and a check valve in a fuel circuit from a pressure accumulating chamber to the needle valve. CONSTITUTION:A fuel injector is provided with a feed pump 2 for always supplying fuel under injection pressure; injection nozzles 10 disposed in cylinders; a pressure intensifying piston 20 for pressurizing a needle valve 22 disposed at the tip end of the injection nozzle 10 when an injection pressure is applied to the injection nozzle 10; a solenoid valve 11 for switching a fuel circuit connected to the pressure intensifying piston 20; a pressure accumulating chamber 30 for accumulating fuel under injection pressure; a check valve 33 disposed in a circuit for supplying fuel of injection pressure to the needle valve 22 from the pressure accumulating chamber 20; and a drain circuit 17 for discharging the fuel. Consequently, the pressure accumulating chamber 20 is always kept under a high pressure, thus eliminating leakage of the fuel and a possibility of fire caused by the leakage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel injection device for a diesel engine.

[0002]

2. Description of the Related Art Conventionally, in a diesel engine fuel injection device, an independent type using a column fuel injection pump,
The joint injection method (common rail injection system) is used, the fuel injection timing is constant,
The injection pressure is also several hundred kg / cm ² .

However, recent fuel injection devices can control the fuel injection timing according to the number of revolutions and the load in order to improve output performance, reduce fuel consumption, improve exhaust color, and purify exhaust gas. That is, a high injection pressure of 1500 kg / cm ² or more can be obtained, the injection pressure is low in the early stage of the injection, the injection pressure is high in the latter stage of the injection, and the fuel is sharply cut from the high pressure state when the valve is closed. It is required that a high injection pressure be obtained even in the low engine speed range and that the valve opening pressure be controllable.

Although various inventions and inventions have been made in response to the above requirements, none of them satisfy the requirements sufficiently. FIG. 6 (a) shows an example of a common rail injection system which is considered to best meet the above requirements. 50 is an oil pan, 51 is a feed pump, and 52 is a high-pressure pump, which can generate a pressure of 1200 kg / cm ² . A pressure accumulating chamber 54 is provided on the circuit 53 that supplies fuel from the high pressure pump 52 to the fuel injection nozzle 60.
Is provided. The injection pressure of the high-pressure pump 52 can be controlled by a control device (not shown).

An electromagnetic valve 61, a valve seat 62, and a drain circuit 63 are provided above the injection nozzle 60, a piston 64 is provided in the middle, and a needle valve 65 is provided below. An injection port 66 is provided at the tip of the injection nozzle 60. The circuit 53 is divided into a circuit 55 to the solenoid valve 61 and a circuit 56 to the needle valve 65.

At the time of no injection, the solenoid valve 6 as shown in FIG.
1, the solenoid valve 61 and the valve seat 62 are closed, and the circuit 5
5, the fuel pressure is applied to the piston 64, the needle valve 65 is pressed downward to close the injection port 66, and the fuel is not injected.

At the time of injection, as shown in FIG. 6B, the solenoid valve 61 is operated to open the solenoid valve 61 and the valve seat 62 to communicate with the drain circuit 63, and to close the circuit 55, the piston 6 is closed.
The pressure of the fuel applied to No. 4 is lowered, the needle valve 65 is pushed up, and high-pressure fuel of 1200 kg / cm ² is injected from the injection port 66.

Therefore, the injection timing can be controlled by the operation timing of the solenoid valve 61, the injection pressure at the initial stage of injection is low,
The injection pressure in the latter part of injection is high. Moreover, when the valve is closed, the high pressure state is sharply cut, and the injection pressure is high even in the low speed range.
It has excellent characteristics such as control of valve opening pressure.

[0009]

However, according to the above construction, since a high pressure of 1200 kg / cm ² is always present in the accumulator, there is a risk of fuel leakage and fire.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection device for a diesel engine which satisfies the above-mentioned various characteristics and can safely obtain a higher injection pressure. There is.

[0011]

[Means for Solving the Problems] To achieve the above object,
1st of the fuel injection device of the diesel engine which concerns on this invention
In a fuel injection device including a feed pump that constantly supplies fuel at an injection pressure, and an injection nozzle attached to each cylinder, the injection nozzle receives the injection pressure and reaches the tip of the injection nozzle. A pressure-increasing piston that pressurizes the needle valve provided, a solenoid valve that switches the fuel circuit to the pressure-increasing piston, a pressure accumulating chamber that stores fuel of injection pressure, and a fuel of injection pressure from the pressure accumulating chamber to the needle valve. The present invention is characterized in that a check valve provided in a supply circuit and a drain circuit for discharging fuel are provided, and in the second invention, when the solenoid valve is operated, fuel having injection pressure is supplied to the booster piston. A valve is provided to close the supply circuit to open the drain circuit, and to open the circuit to supply the injection pressure fuel to the pressure boosting piston to close the drain circuit when the operation is stopped. It is characterized in that.

[0012]

According to the above structure, the fuel injection nozzle of the fuel injection device having the feed pump that constantly generates the injection pressure is provided with the booster piston for pressurizing the needle valve with the injection pressure and the booster piston during operation. The fuel valve is closed and the drain circuit is opened, and when the operation is stopped, a solenoid valve that opens the fuel circuit to the booster piston and closes the drain circuit, a pressure accumulation chamber, and a check valve in the fuel circuit from the pressure accumulation chamber to the needle valve are provided. Since the solenoid valve is provided, the booster piston communicates with the drain circuit when the solenoid valve is activated, and the needle valve rises due to the injection pressure of the feed pump to open the injection port and inject fuel. When the operation of the solenoid valve is stopped, the booster piston receives the injection pressure and pressurizes the needle valve. Therefore, the fuel is injected at a higher injection pressure than the initial injection pressure, and the injection is completed when the needle valve descends and closes the injection port.

[0013]

Embodiments of the fuel injection device for a diesel engine according to the present invention will be described below in detail with reference to the drawings. FIG. 1A is a schematic view of a fuel injection device, 1 is an oil pan, 2 is a fuel feed pump, 3 is a pressure control valve having a valve 4, 5 is a pressure detection sensor, and 6 is a control device.

A solenoid 12 is provided above the injection nozzle 10.
And a solenoid valve 11 including a valve 13 having a hole 14 and a spring 15. Below the solenoid valve 11, a pressure accumulator chamber 3 is supplied with fuel having an injection pressure from the feed pump 2.
0 and a cylinder 16 for accommodating the booster piston 20 are provided.

The pressure boosting piston 20 is biased downward by a spring 21, and its lower end abuts a needle valve 22 to close an injection port 23.

A check valve 33 is provided in the passage 31 that connects the pressure accumulating chamber 30 and the needle valve chamber 32, and the fuel flows only from the pressure accumulating chamber 30 to the needle valve chamber 32.

In the solenoid valve 11, when the solenoid 12 is not operating, the valve 13 is biased upward by the spring 15, the drain circuit 17 is closed at the upper end, and the pressure accumulation chamber 3 is formed at the lower end.
The passages to 0 and cylinder 16 are open. At this time, the pressure accumulating chamber 30 and the cylinder 16 are in communication with each other. Therefore,
The booster piston 20 receives the injection pressure and is pressed downward.

When the solenoid 12 is operated, the valve 13 moves downward against the spring 15 and the pressure accumulating chamber 30 and the cylinder 16 are moved.
Close the circuit with and open the drain circuit 17 to open the hole 1 of the valve 13.
4, the cylinder 16 and the drain circuit 17 are communicated with each other.

Next, the operation will be described. FIG. 2 shows a state immediately before the start of fuel injection. The feed pump 2 constantly feeds fuel having an injection pressure, for example, a pressure of 610 kg / cm ^{2 to} the pressure accumulating chamber 30. This pressure is controlled by the control device 6
Can be changed by controlling the opening of the valve 4 of the pressure control valve 3.

When the solenoid 12 is operated by a signal from a control device (not shown), the drain circuit 17 is opened, and the fuel having the injection pressure in the cylinder 16 escapes to the drain circuit 17 so that the relief pressure becomes zero. Since the needle valve chamber 32 has a residual pressure higher than the injection pressure of the feed pump 2, the needle valve 22 receives an upward force and rises as shown in FIG.
The injection port 23 opens to start fuel injection.

The fuel pressure in the passage 31 and the needle valve chamber 32 decreases due to the volume increase due to the rise of the needle valve 22 and the fuel injection. Therefore, the fuel of the injection pressure sent from the feed pump 2 pushes the check valve 33 open and is sent to the needle valve chamber 32 through the passage 31 and injected from the injection port 23. That is, the injection pressure while the needle valve 22 is rising is 610 kg / cm ² .

Next, as shown in FIG. 4, when the operation of the solenoid 12 is stopped, the valve 13 moves upward and the drain circuit 1
7 is closed, the pressure accumulating chamber 30 and the cylinder 16 are communicated with ^each other, and a pressure of 610 kg / cm ² is applied to the pressure increasing piston 20.

In this embodiment, the area of the D portion of the booster piston 20 shown in FIG.
3 times the area of the part. Also, the spring 21 is 250 kg / cm
^With a set load equivalent to ^2, the downward force of the booster piston 20 is equivalent to 2000 kg / cm ² . Check valve 3 at this time
Since 3 is closed, the injection pressure when the needle valve 22 descends is 2000 kg / cm ² .

The needle valve 22 continues to move downward,
The injection port 23 is closed as shown in FIG. At this time, 2000 kg in the passage 31 and the needle valve chamber 32.
/ Cm ² residual pressure remains, and the injection nozzle 10 is closed and held.

[0025]

As described in detail above, according to the present invention, an injection nozzle of a fuel injection device of a diesel engine equipped with a feed pump that constantly supplies fuel at an injection pressure receives an injection pressure to pressurize a needle valve. Provided in the pressure piston, the solenoid valve that controls the opening and closing of the drain circuit and the circuit that supplies fuel of injection pressure to the booster piston, the accumulator chamber that stores fuel of injection pressure, and the fuel supply circuit from the accumulator chamber to the needle valve. Since it has a check valve, the following effects are achieved. (1) The injection timing can be controlled according to the rotation speed and the load. (2) 1500 from the latter stage of injection to the valve opening
A high injection pressure of kg / cm ² or more can be obtained. (3) Since the injection pressure in the initial stage of injection can be lowered and the injection pressure in the latter stage of injection can be raised, the combustion temperature can be lowered and the generation of NOx can be reduced. (4) Since the high injection pressure is sharply cut when the valve is closed, there is no fuel dripping and the exhaust color is good. (5) It is possible to obtain a high injection pressure from a low speed range, improve exhaust color at low speeds and high loads, and secure low speed torque. (6) The valve opening pressure can be controlled. (7) Since the pressure accumulating chamber is built in the injection nozzle, there is no risk of fuel leakage.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a fuel injection device of the present invention.

FIG. 2 is a schematic diagram showing a state immediately before the start of injection in the fuel injection device of the present invention.

FIG. 3 is a schematic diagram showing a state of injection start of the fuel injection device of the present invention.

FIG. 4 is a schematic diagram showing a state immediately before the end of injection of the fuel injection device of the present invention.

FIG. 5 is a schematic diagram showing a state of injection completion of the fuel injection device of the present invention.

FIG. 6 is a schematic view of a conventional fuel injection device.

[Explanation of symbols]

 2 feed pump 3 pressure control valve 6 control device 10 injection nozzle 11 solenoid valve 13 valve 14 hole 16 cylinder 17 drain circuit 20 pressure boosting piston 22 needle valve 23 injection port 30 accumulator chamber 31 passage 32 needle valve chamber 33 check valve

Claims (2)

[Claims] 1. A fuel injection device comprising a feed pump for constantly supplying fuel at an injection pressure and an injection nozzle mounted in each cylinder, wherein the injection nozzle receives injection pressure and reaches the tip of the injection nozzle. A pressure-increasing piston that pressurizes the needle valve provided, a solenoid valve that switches the fuel circuit to the pressure-increasing piston, a pressure accumulating chamber that stores fuel of injection pressure, and a fuel of injection pressure from the pressure accumulating chamber to the needle valve. A fuel injection device for a diesel engine, comprising a check valve provided in a supply circuit and a drain circuit for discharging fuel. 2. A circuit for supplying a fuel having an injection pressure to the pressure boosting piston by closing the drain circuit by opening the drain circuit when the solenoid valve operates, and a circuit for supplying a fuel having an injection pressure to the pressure boosting piston when the operation is stopped. 2. The fuel injection device for a diesel engine according to claim 1, further comprising a valve that opens the valve to close the drain circuit.