JP3372325B2 - Diesel engine fuel injection system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for a diesel engine. 2. Description of the Related Art A conventionally known mechanically driven electronic control unit injector will be described with reference to FIG. Reference numeral 01 denotes a plunger for pumping fuel, and reference numeral 02 denotes a body in which the plunger slides while maintaining oil tightness and accommodates other parts. Reference numeral 03 denotes a poppet valve, which determines the start and end of fuel discharge from the nozzle based on the closing and opening timings of the poppet valve. A solenoid 04 drives the poppet valve 03. 05 is the return spring of the poppet valve 03, 0
A fuel oil passage 6 communicates the plunger chamber with the poppet valve. 08 is a poppet valve room, 09 is a plunger room, 01
0 is a nozzle tip, 011 is a nozzle nozzle, 012 is a needle valve, 013 is a nozzle spring, 014 is a shim for setting the valve opening pressure of the nozzle, 015 is a spring receiver, 016 is a fuel oil path connecting the plunger chamber and the nozzle, 017 is a tappet, 018 is a plunger spring, 019 is a controller, 020 is a drive unit, and 21 is a nozzle oil reservoir. Next, the operation of the conventional example will be described.
The tappet 017 and the plunger 01 combined therewith are driven via a cam, a push rod, and a rocker arm (not shown) which are driven in synchronization with a crankshaft (not shown). During the lift stroke of the plunger 01, the solenoid 04 closes the poppet valve 03 according to a command from the controller 019. Then, the fuel in the plunger chamber 09 is compressed, and the pressure is transmitted to the oil reservoir 019 of the nozzle tip 010 through the fuel oil passage 016. When this pressure becomes higher than a preset nozzle opening pressure, the needle valve 012 is pushed up, and high-pressure fuel is injected from a nozzle injection port 011 into an engine cylinder (not shown). Further, while the plunger 01 is being lifted, the power supply to the solenoid 04 is cut off by a command from the controller 019. Then, the electromagnetic force that tries to hold the poppet valve 03 closed disappears, and the poppet valve 03
Is opened by the action of the return spring 05. As a result, the high-pressure fuel is discharged outside through the fuel oil passages 06 and 07. For this reason, the pressure in the oil sump 021 of the nozzle tip 010 decreases, and the needle valve 012 moves to the nozzle spring 013.
To descend, sit down, and the fuel injection ends. FIG. 2A shows an injection phenomenon caused by a conventional unit injector or a jerk type fuel injection device. Injection characteristics of the diesel engine is generally were as shown in the figure, the measure the performance of the engine by increasing the injection pressure P _f, it is necessary to shorten the injection crank angle theta _f. For this reason, measures are taken to increase the oil feed rate of the plunger 1. However, if such measures are taken, engine performance such as fuel consumption and smoke emission will be improved, but diesel knock will be generated and the combustion gas will not be smooth, resulting in an increase in noise. In particular, when a fuel having a low cetane number is used, the disadvantage becomes significant. As a countermeasure, a small amount of fuel is injected as an ignition source before the main injection, so that the ignition combustion process is smoothed to realize quiet combustion. This injection situation is shown in FIG. That is, the above-mentioned injection is called a pilot injection, which is a desirable injection method for preventing diesel knock and for improving the performance and reducing the pollution of the diesel engine. However, when the pilot injection is to be realized for a mechanically driven electronic control unit injector, the following problem occurs. That is, in order to realize the pilot injection and the main injection, it is necessary to repeatedly close and open the poppet valve twice during a very short period. The fuel metering of this type of fuel injector is defined by the closing and opening of the poppet valve,
The poppet valve response speed is i) the lower limit of the injection amount that can be injected stably every cycle ii) limits the interval between the pilot injection and the main injection. That is, there is a problem that the stability of the minute amount injection is impaired, and a problem that the flexibility of controlling the timing and the amount of the pilot injection is impaired. It is an object of the present invention to inject fuel at a high pressure and smoothly promote combustion after ignition, to stabilize fuel metering for pilot injection, and to adjust the injection timing. An object of the present invention is to provide a highly flexible fuel injection device that can be freely controlled. A fuel injection device for a diesel engine according to the present invention has a plunger chamber (9) formed at the head of a plunger (1) for feeding fuel and an injection nozzle (10). And a fuel oil passage (16) communicating the plunger chamber with a poppet valve chamber (8) facing the poppet valve (3). Poppet with control unit injector
By repeating valve closing and opening twice, before the main injection
Pilot injection by injecting a small amount of fuel as an ignition source
The fuel injection system for a diesel engine was Migihitsuji, the fuel oil path branching oil path branched from the middle of a (6) and (21), a piston chamber which is communicated with the branch oil passage (0
24), provided between the branch oil passage and the piston chamber.
A disk orifice with a throttle (22) and the branch
Guided from the oil passage through the disk orifice to the piston chamber
A hydraulic piston (24) moved by the fuel oil pressure, a spring (26) provided on the back side of the hydraulic piston for setting the operating pressure of the hydraulic piston to a pressure lower than the valve opening pressure of the injection nozzle, and the hydraulic piston the stopper (27) that limits the amount of movement of the volume increase side provided the hydraulic piston on the back, the leakage oil than the sliding portion of the front Symbol communicated from the rear chamber of the hydraulic piston to drain the hydraulic piston returned back to the drain and an oil passage (30), the pilot injection
When the poppet valve is opened for the first time,
The fuel oil pressure guided to the piston chamber through the square orifice
The hydraulic piston moves to the stopper position
The nozzle absorbs a part of the fuel discharged from the plunger, and
Reducing the injected fuel delivered to the oil sump (31)
After the pilot injection, the poppet valve closes again and
When performing the valve opening operation for injection, the hydraulic piston
Contact the stopper to maintain a certain position.
Sign . In the mechanically driven electronic control unit injector shown in FIG. 1, the poppet valve 3 is closed as shown in FIG. 3 (a) by a command from the controller 19 during the driven stroke.・ Opening is performed twice, that is, opening → closing → opening → closing → opening. In this case, operation A
Corresponds to the pilot injection, and the operation B corresponds to the main injection. In order to operate the former with good stability every cycle, as shown in FIG.
It is necessary to close the poppet valve 3 once and then immediately open it. However, in this case, since the response speed of the solenoid 4 and the poppet valve 3 has a limit value, the injection amount during the stable limit lift of the poppet valve 3 metered by the operation of the poppet valve 3 is a small pilot injection required for combustion performance. Larger than the quantity. Therefore, in order to reduce the injection amount, the hydraulic piston 24 is operated as shown in FIG. 3 (b), so that the newly installed hydraulic piston causes an increase in the volume of the piston chamber accompanying the operation, whereby the plunger causes Absorbs part of the discharged fuel. As a result, the amount of fuel finally delivered to the nozzle oil sump 31 is reduced as compared with that of the conventional device, and the fuel amount corresponds to the required minute injection. As a result,
As shown in FIG. 3C, a small amount of pilot injection is stably realized. After the pilot injection is completed, the poppet valve performs the closing / opening operation B again. At this time, the hydraulic piston 24 is constant at the position where it hits the stopper, and does not absorb the fuel discharged from the plunger. An injection is performed. After the main injection, the hydraulic piston 2
4 descends slowly due to a disk orifice 22 with a throttle provided between the branch oil passage 21 and the piston chamber. At this time, since the poppet valve 3 is fully opened, There is no such a problem that the nozzle needle valve is raised again by the operation. As a result of the operation of the newly provided hydraulic piston 3, a small amount of pilot injection is stably performed at an appropriate timing before the main injection, so that diesel knock is suppressed. Pollution can be achieved. An embodiment of the present invention will be described below with reference to FIG. In the figure, 1 to 20 are 01 to 020 of the conventional example.
Therefore, the description is omitted. Next, the features of the present invention will be described. A branch oil passage 21 is newly provided in the middle of the fuel passage 6 that connects the plunger chamber 9 and the poppet valve chamber 8.
The branch oil passage 21, the hydraulic piston 24 is provided in the hydraulic cylinder device further injects movement starting pressure of the hydraulic piston 24 on the back side of the hydraulic piston 24 nozzles 1
A spring 26 for setting a pressure lower than the valve opening pressure of 0 is provided. 22 is a disk orifice with a throttle,
25 is a spring receiver, 27 is a stopper for limiting the lift of the hydraulic piston 24, 28 is a piston holder in which the hydraulic piston 24 slides, 29 is a holder that wraps the piston holder 28 , and 30 is a leak from the periphery of the hydraulic piston 24. A return oil path 31 for returning oil to the drain is a nozzle oil reservoir. 024 is a piston facing the hydraulic piston 24
Room. Next, the operation of the above embodiment will be described.
In order to perform the pilot injection in the mechanically driven electronic control unit injector shown in FIG. 1, the poppet valve 3 is closed and opened by a command from the controller 19.
Have to be operated twice. In this case, in FIG. 3A, the operation A corresponds to the pilot injection, and the operation B corresponds to the main injection. In order to operate the former with good stability in each cycle, it is necessary to open the poppet valve 3 once at the portion A and then immediately open the valve seat as shown in FIG. However, in this case, since the poppet valve 3 mainly has inertia, the poppet valve 3 cannot correspond to the injection amount required for pilot injection, and the injection amount becomes excessive. Therefore, in order to reduce the injection amount, in the present invention, a hydraulic piston 24 is newly provided as shown in FIGS. 1 and 3 (b), so that the volume of the piston chamber 024 caused by the movement of the nuclear hydraulic piston 24 is increased. Part of the discharged fuel is absorbed, whereby the injected fuel delivered to the nozzle oil sump 31 is reduced as compared with the conventional device. As a result, an appropriate stable pilot injection can be realized as shown in FIG. After the pilot injection is completed, the poppet valve 3 performs the closing / opening operation B again. At this time, the hydraulic piston 24 abuts against the stopper 27 and maintains a fixed position, so that the fuel discharged from the plunger 1 is absorbed. No effect on high-pressure main injection. After completion of the main injection, the hydraulic piston 24 recovers, but moves slowly due to the throttled disk orifice 22 provided between the branch oil passage 21 and the piston chamber. Since it is open, the nozzle needle valve is not restarted due to the restoration of the hydraulic piston, and there is no problem such as leakage afterward. Thus, by the action of the newly installed hydraulic piston 3, a small amount of pilot injection is stably performed at an appropriate timing before the main injection, diesel knock is sufficiently suppressed, and high performance and low pollution of the diesel engine are achieved. realizable. Although the above embodiment has been described with reference to an electronic unit injector, the present invention is also applicable to a jerk type fuel injection device. According to the present invention, a part of the fuel injected into the nozzle oil reservoir during the pilot injection is absorbed and reduced by the action of the newly installed hydraulic piston, and a very small amount of pilot injection is performed with good timing. At the same time, there is no adverse effect on the subsequent high-pressure main injection. As a result, there is no diesel knock, low fuel consumption, low smoke emission and low NOx,
A low-noise, high-performance diesel engine can be realized. In addition, even when a low cetane number fuel is used, smooth combustion can be realized, so that fuel cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sectional view of a unit injector according to a first embodiment of the present invention and a system diagram of an entire system. FIGS. 2A and 2B show injection characteristics of a fuel injection device, wherein FIG. 2A shows a conventional example and FIG. FIG. 3 is a diagram showing the relationship between the operation of main components (poppet valve, hydraulic piston) of the present invention and injection characteristics. FIG. 4 is a sectional view showing a conventional unit injector. [Explanation of Signs] 1 ... Plunger for pumping fuel, 2 ... Body, 3 ... Poppet valve, 4 ... Solenoid, 5 ... Return spring, 6
… Fuel passage (connecting plunger chamber and poppet valve chamber),
7 ... fuel passage (connecting the poppet valve chamber and the fuel tank),
8 poppet valve chamber, 9 plunger chamber, 10 nozzle tip, 11 nozzle nozzle, 12 needle valve, 13 nozzle spring, 14 shim, 15 spring receiver, 16 fuel passage (plunger chamber and nozzle 17) Tappet, 18 ... Plunger spring, 19 ... Controller, 20 ... Drive unit, 21 ... Branch oil passage, 22 ...
Disc orifice (having a throttle), 23 ... spring, 24 ... hydraulic piston, 25 ... spring receiver, 26 ...
Spring, 27: stopper (limits lift of hydraulic piston), 28: piston holder, 29: holder, 3
0 ... (leak fuel) return oil passage.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) F02M 57/02 330 F02M 57/02 310 F02M 45/04

Claims (1)

(57) [Claims] 1. A head of a plunger (1) for pumping fuel.
Plunger chamber (9) and injection nozzle (10)
A fuel oil passage (16) communicating with an oil sump (31) of the
Poppet valve room facing plunger room and poppet valve (3)
Electronic control provided with a fuel oil passage (6) communicating with (8)
Having a unit injector,Closing and opening poppet valves
Is repeated twice to reduce ignition source before main injection.
Pilot injection is performed by injecting the amount of fuelDe
In fuel injectors for diesel engines, Way of the fuel oil passage (6)Branched from insideBranch oilway (2
1) andThe piston chamber (02) communicating with the branch oil passage
4) and provided between the branch oil passage and the piston chamber.
A disk orifice with a throttle (22) and the branch oil
From the path to the piston chamber through the disc orifice
Move by fuel oil pressureA hydraulic piston (24) and the oil
The operating pressure of the hydraulic piston is provided behind the pressure piston.
A spring set at a pressure lower than the valve opening pressure of the injection nozzle.
(26) and the oil provided on the back side of the hydraulic piston.
Stopper that limits the amount of movement of the pressure piston to the volume increase side
(27) and,PreviousFrom the rear chamber of the hydraulic piston to the drain
To drain oil from the sliding part of the hydraulic piston.
And a return oil passage (30) for return, At the first opening of the poppet valve for the pilot injection
Piston chamber from the branch oil passage through disc orifice
The hydraulic piston guided by the hydraulic pressure
Part of the fuel discharged from the plunger
Which is absorbed and sent to the nozzle oil sump (31)
In addition to reducing fuel,
When the valve opens again for closing and main injection
Then, the hydraulic piston comes into contact with the stopper and
Diesel engine fuel characterized by maintaining
Injection device.