JPS6016777Y2 - Diesel engine fuel injection system - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of an electronically controlled fuel injection device for electrically controlling the amount of fuel injected in a diesel engine.

Conventionally, in this type of fuel injection device, in order to prevent the fuel remaining in the cup from dripping into the combustion chamber after fuel injection, the residual fuel is sucked back to the metering valve side by a post-injection suck-back circuit. What has been done is known.

However, in conventional sucking back circuits, the shock waves generated during sucking back directly hit the metering valve, which caused problems such as causing the metering valve to malfunction.

This invention was made for the purpose of improving this problem, and provides a fuel injection device for a diesel engine in which the metering valve is a three-way valve so that the outlet side passage communicates directly with the spill passage during sucking back. This is intended to prevent the metering valve from being damaged by shock waves generated during suction.

This invention will be described in detail below with reference to an illustrated embodiment.

In the figure, 1 is an injection nozzle provided for each combustion chamber of a diesel engine (not shown), and there is a servo cylinder 2 inside.
A servo piston 4 for driving a plunger 3 is housed within this servo cylinder 2.

Reference numeral 5 denotes a servo valve that controls the operating pressure supplied to the servo cylinder 2, and has an excitation coil 6, and when the excitation coil 6 is energized, the spool 7 is slid. .

A small diameter portion 7a is formed in the spool 7, and is configured to communicate with and shut off a port 7b leading to a high-pressure pump (not shown) and a port 7c leading to the servo cylinder 2.

On the other hand, 8 is an electronically controlled metering valve and the valve body 8
It has a spool 8b inside a, and communicates with and is cut off from three ports 81°, 8□ and 83 provided around the spool 8b.

Port 81 is connected to a low pressure pump (not shown),
Low-pressure fuel is supplied, and during metering, this fuel flows into the port 8□ communicated with the small diameter portion 8C of the spool 8b, and the port 8□ is connected to the passage 9 and the check valve. It communicates with the bottom of the plunger chamber 3a via 10.

Further, the port 83 is closed by the spool 8b during metering, and is communicated with the port 8° during fuel suction, so that the sucked back fuel can be discharged to the spill passage 11 side.

On the other hand, the bottom of the plunger chamber 8a is communicated with the cup 1a at the tip of the injection nozzle 1 through a separate passage 12.

An injection hole 1b that is closed by a needle valve 13 is provided at the tip of the cup 1a, and the needle valve 13 is opened against a spring 14 that biases the needle valve 13 as the pressure inside the cup 1a increases. Plunger chamber 3a and cup 1a
The fuel inside is injected into the combustion chamber from the injection hole.

Further, a small diameter portion 3b is formed in the center of the plunger 3.

This small diameter portion 3b is communicated with the return passage 15 at the lower limit of the stroke of the plunger 3.

The return passage 15 joins the passage 9 between each of the check valves 10 and 11, and the plunger chamber 3a and the return passage 15 are communicated through a passage 3C provided in the plunger 3.

Note that 16 is a drain passage. The low-pressure fuel supplied to the metering valve 8 from a low-pressure pump (not shown) flows into the passage 9 through the ports 81 and 82 communicated by the small-diameter portion 8c of the spool 8b, and is passed through the check valve 10 by the passage 9. and flows into the plunger chamber 3a.

Subsequently, the servo valve 5 is activated by a command from a control circuit (not shown).
When the excitation coil 6 is energized, the spool 1 moves upward and communicates the ports 7b and 7c, so high-pressure hydraulic oil flows into the servo cylinder 2 and moves the plunger 3 downward via the servo piston 4. let

As a result, the fuel filled in the plunger chamber 3a is pressurized, and the pressurized fuel reaches the inside of the cup 1a through the passage 12, opens the needle valve 13, and is simultaneously injected into the combustion chamber from the injection hole 1b. be done.

When the plunger 3 reaches its lower limit, the small diameter portion 3b of the plunger 3 matches the return passage 15, and the plunger chamber 3a and the return passage 15 communicate with each other via the passage 3c in the plunger 3.

As a result, when the needle valve 13 is closed, the fuel remaining in the passage 12 and the cup 1a flows back toward the passage 9, ie, is sucked back.

At this time, a shock wave is generated, and this shock wave spreads to the metering valve 8 through the passage 9. At this time, since the port 8□ and the port 83 are communicated in the metering valve 8, the shock wave is transmitted to the port 83. Since the water passes through the spill passage 11, it does not have any adverse effect on the metering valve 8.

This idea uses three metering valves as detailed above.
As a directional valve, when sucking back fuel, the outlet side port is communicated with the port leading to the spill passage.
The shock waves generated during suction pass directly into the spill passage, making it possible to prevent the metering valve from being damaged by shock waves.

In addition, because a part of the passage and the port of the metering valve are shared during metering and suction,
Compared to a system in which metering and suction are performed in separate circuits, the overall structure can be simplified, with fewer valves and passages required.

[Brief explanation of the drawing]

The drawing is a block diagram showing an embodiment of this invention. 1 is an injection nozzle, 1a is a cup, 1b is an injection hole, 3 is a plunger, 3a is a plunger chamber, 5 is a servo valve, 8 is a metering valve, 81 to 83 are ports, 9 is a passage, 11 is a spill passage, 13 is a needle valve.

Claims (1)

[Scope of utility model registration request] The plunger 3 in the injection nozzle 1 is driven by high-pressure hydraulic oil supplied via an electronically controlled servo valve 5 to pressurize the fuel in the plunger chamber 3a, and this pressurized fuel pressure causes injection. The needle valve 13 that closes the hole 1b is opened to inject fuel into the fuel chamber, and 1. As the plunger 3 descends, the fuel remaining in the cup 1a and the plunger chamber 3a after injection is transferred to the suction return passage 15 communicating with the plunger chamber 3a through a passage 3c formed in the plunger 3 and the plunger chamber 3a. In the case where the suction is returned to the metering valve 8 side through a passage 9 connecting between the metering valves 8, the metering valve 8 is connected to the plunger chamber 3a through the port 8□ leading to the low pressure pump and the passage 9. at least three ports 8° leading to the spill passage 11 and a port 83 leading to the spill passage 11;
This fuel injection device for a diesel engine is a directional valve, and ports 81 and 8° communicate with each other during metering, and ports 8□ and 83 communicate with each other during suction.