JPH04339167A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To attain high performance such as low fuel consumption, little smoke, and low noise by providing a control device with which a piezoelectric actuator is energized synchronizing with rotation of an engine and main fuel injection and pilot injection are performed, and a check valve to prevent back flow provided on a main fuel passage. CONSTITUTION:A needle valve 12 is pushed up by pressure, and fuel is injected from nozzles 11 through a vale seat. This fuel injection becomes a pilot injection. By removing voltage, because a voltage actuator element 21 is returned to an original position and a piston 22 is pulled, pressure of a fuel passage 23 is lowered and a check valve 31 is opened by fuel from a fuel feed pump 32, and fuel is fed to the extreme end chamber of the piston 22. Back flow of fuel flowing in from a fuel passage 16 is obstructed by a check valve 24. Next, main injection of fuel is performed by control with a controller 19. Because the pilot injection system is provided independently of the main injection system, injection characteristics respectively suitable for the main injection and the pilot injection can be realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a fuel injection system for a diesel engine.

0002

2. Description of the Related Art A conventional mechanically driven electronic control unit injector will be explained with reference to FIG. In addition to this, conventional technology also includes the Bosch type, which consists of a fuel injection pump, an injection pipe, and an injection valve. FIG. 3 is a cross-sectional and complete system diagram of a mechanically driven electronic control unit injector. In the figure, 01 is a plunger, and 02 is a body with a barrel hole in which the plunger 01 reciprocates in an oil-tight manner and supports other parts. A poppet valve 03 is provided in the body and is always away from the valve seat. A solenoid 04 is provided outside the valve stem end of the poppet valve 03. 05 is a return spring and the poppet valve 03
is pushing the valve stem end.

A plunger chamber 09 is provided in the body 02. 08 is the poppet valve chamber and the poppet valve 0
This is the chamber on the valve stem side of No. 3. Reference numeral 021 denotes a valve cap chamber, which is a chamber outside the valve cap of the poppet valve 03. A fuel passage 06 communicates the plunger chamber 09 with the poppet valve chamber 08. 07
A fuel passage communicates the valve body chamber 026 with an undisclosed fuel tank. A nozzle tip 010 is provided at the tip of the body, has a hole in the center, and has a conical valve seat at the tip. 011 is a hole drilled at the tip of the nozzle tip 010 for nozzle injection, etc.

Reference numeral 012 denotes a needle valve that is oil-tightly fitted into the hole of the nozzle tip 010, and its tip is always in contact with the conical valve seat of the nozzle tip 010. A nozzle spring 013 presses the upper end surface of the valve stem of the needle valve 012 via a spring catch. A shim 014 is provided between the nozzle spring 013 and the body 02. A fuel passage 016 communicates the plunger chamber 09 with the oil reservoir of the nozzle tip 010. 017 is a tappet provided on the end face of the plunger 01. 018 is a plunger spring and is provided between the body 02 and the tappet 017. 019 is a controller, and 020 is a drive unit which is connected to the controller 019 and to the solenoid 04.

Next, the operation of a mechanically driven electronically controlled unit injector of the prior art will be explained. The plunger 01 combined with the tappet 017 is pushed through a cam (not shown), a tappet, a push rod, and a rocker arm (not shown) that are driven in synchronization with the rotation of a crankshaft (not shown). While the plunger 01 is moving forward, the solenoid 0 is activated by the drive unit 020 in response to a signal from the controller 019.
4 is energized, it pulls the poppet valve 03 toward the valve stem so that the poppet valve seats and closes the fuel passage 06. As a result, the plunger chamber 07 is sealed and the internal pressure increases.The pressure is transmitted to the nozzle tip 010 through the fuel passage 016 and acts on the tip of the needle valve 012, and the pressure is applied to the nozzle spring 0.
13, the fuel pushes up the needle valve 012 against the force of the nozzle spring 013 and is ejected from the nozzle outlet 011.

Next, when the current from the drive unit 020 to the solenoid 04 is cut off by a signal from the controller 019 while the plunger 01 is moving forward,
The force of the solenoid 04 to pull the poppet valve 03 disappears, and the poppet valve 03 leaves the valve seat due to the force of the return spring 05, so the fuel passage 06 opens to the valve cap chamber 021, and when the seal in the plunger chamber 09 is broken and the pressure decreases, The pressure at the tip of the needle valve 012 also decreases, and the force of the nozzle spring 013 overcomes, pushing the needle valve 012 back to its seat and stopping the injection of fuel. Thereafter, the fuel pushed away by the plunger 01 passes through the fuel passage 06, the valve bulk chamber 021, and the fuel passage 07, and is discharged to a fuel tank (not shown).

[0007]

The diagram of FIG. 2(a) shows an injection situation by a conventional unit injector or Bosch type fuel injection device. Generally, the fuel injection situation of a diesel engine is as shown in FIG. 2(a), and in order to improve the performance of the engine, it is necessary to increase the injection pressure Pf and shorten the injection period θf. For this reason, measures such as increasing the oil delivery rate of the plunger are taken. However, as a result, although engine performance such as fuel efficiency and smoke emissions is improved, combustion becomes less smooth, resulting in diesel knock and increased noise. This drawback is particularly noticeable when using fuel with a low cetane number. As a countermeasure to this, if a small amount of fuel is injected as an ignition source just before the main injection, the ignition combustion process can be smoothed and quiet combustion can be achieved. This injection situation is shown in FIG. 2(b). However, when attempting to realize such pilot injection using both injection systems, the following problems occur.

(1) Unit injector type fuel injection device. When implementing pilot injection with the mechanically driven electronic control unit injector described above, it is necessary to open and close the poppet valve twice within a very short period of time. Therefore, depending on the response speed of the poppet valve, (i) the lower limit of the injection amount that can be stably injected every cycle (i
i) The interval between pilot injection and main injection is limited. That is, there are problems such as the stability of micro-injection being impaired and the flexibility of controlling the timing and amount of pilot injection being impaired.

(2) Bosch type fuel injection device. When implementing pilot injection with this injection system, the following method is used. (i) The lift curve of the cam is devised to create a speed mode that discharges in two stages. or (ii) an injection pump or injection pipe for pilot injection;
A new injection valve will be installed to create a 2-pump, 2-nozzle injection system. In these cases as well, a problem arises in that the interval between pilot injection and main injection cannot be freely controlled.

The object of the present invention is to provide a system that injects fuel at high pressure and high injection rate and achieves smooth combustion after ignition, with stable fuel metering for the pilot injection and also with flexible injection timing. The objective is to provide a controllable and highly flexible injection system.

[0011]

[Means for Solving the Problems] A fuel injection device for a diesel engine includes a fuel passage communicating with a nozzle fuel reservoir adjacent to a seat portion of a fuel injection nozzle needle valve, and a piston provided in a part of the fuel passage. a piezoelectric actuator provided behind the piston; a check valve provided in the fuel passage that allows flow only from the piston toward the nozzle; a power supply device that drives the piezoelectric actuator; The present invention is characterized by comprising a control device that performs main fuel injection and pilot injection by synchronizing energization with engine rotation, and a check valve provided in the main fuel passage to prevent backflow.

0012

[Operation] When voltage is applied to the piezoelectric actuator by a signal from the controller before main fuel injection, the piezoelectric actuator extends and pushes the piston, and the piston pushes the fuel in the chamber beyond the piston, so the pressure rises and the newly installed The fuel passes through a check valve and reaches the fuel reservoir in the nozzle.
The piezoelectric actuator overcomes the spring force pushing the needle valve and pushes the needle valve up, and the piezoelectric actuator moves for a certain length and then stops. When the voltage applied to the piezoelectric actuator is removed by a signal from the controller, the piezoelectric actuator returns to its original shape. Since the piezoelectric actuator is displaced with very high responsiveness, the metering stability of minute injection quantities is good, and the interval from the main injection can be adjusted freely. As a result, a small amount of pilot injection is stably performed at an appropriate timing before the main injection.

[0011]

Embodiments Next, embodiments of the present invention will be described with reference to FIGS. 1 and 2. 1 is a sectional view and a complete system diagram of a unit injector according to an embodiment of the present invention, FIG. 2 is a characteristic curve diagram, and FIG.
b) is an injection characteristic diagram of an embodiment of the present invention. In the figure, 1 is a plunger, and 2 is an injection pump main body, in which the plunger 1 moves reciprocally through a barrel hole therein, and the injection pump forms the entire skeleton. Reference numeral 3 denotes a poppet valve, which is provided in the injection pump main body 2 and is always separated from the valve seat. A solenoid 4 is provided outside the end of the valve stem of the poppet valve 3. 5 is a return spring that connects the poppet valve 3
is pushing the end face of the valve stem.

Reference numeral 9 denotes a plunger chamber, which is connected to the injection pump main body 2.
This is a chamber in which the plunger 1 moves back and forth. A poppet valve chamber 8 is a chamber on the valve stem side of the poppet valve 3. Reference numeral 34 denotes a valve cap chamber, which is a chamber outside the valve cap of the poppet valve 3. A fuel passage 6 communicates the plunger chamber 9 with the poppet valve chamber 8. 7 is a fuel passage which connects to the valve chamber 34;
is connected to a fuel tank (not shown). 10 is a nozzle tip that constitutes the tip of the fuel injection pump, and has a conical valve seat at the tip. Reference numeral 11 denotes a nozzle, which is a hole formed at the tip of the nozzle tip 10. 12 is a needle valve and the nozzle tip 10
It fits loosely and oil-tight into the center hole of the valve, and the tip always touches the conical valve seat.

A nozzle spring 13 pushes the end face of the needle valve 12. A shim 14 is provided between the nozzle spring 13 and the injection pump main body 2. A spring receiver 15 is provided between the nozzle spring 13 and the needle valve. A fuel passage 16 communicates the plunger chamber 9 with the nozzle tip 10. 1
A tappet 7 is provided on the end face of the plunger 1. Reference numeral 18 denotes a plunger spring, which is provided between the main body 2 and the tappet 17 of the injection pump.

A controller 19 controls fuel injection. 20 is a drive unit to which the controller 19 is connected. A piezoelectric actuator element 21 is attached to the injection pump body. A piston 22 is provided at the end of the piezoelectric actuator 21 and is fitted into a hole in the injection pump body 2. A fuel passage 23 communicates with a chamber at the tip of the piston 22. A check valve 24 is provided at the end of the fuel passage 23 and allows flow only from the piston 22 toward the nozzle.

Reference numeral 25 denotes a spring, which is provided on the check valve 24. A fuel passage 26 communicates the check valve 24 with the fuel reservoir of the nozzle tip 10. A check valve 27 is provided in the fuel passage 16 and allows only flow toward the nozzle tip 10. Reference numeral 28 is a spring and is provided on the check valve 27 with a pressure spring. 29 is an amplifier to which the controller 19 is connected. 30 is a power supply for driving the piezoelectric actuator, and is connected to the amplifier 29. 3
3 is a fuel tank, and 32 is a fuel supply pump that communicates with the fuel passage 23. A check valve 31 is located between the fuel supply pump 32 and the fuel passage 23 and allows only flow from the fuel supply pump 32.

Next, the operation of the above embodiment will be explained. The controller 19 sends a signal to the amplifier 29 before the main fuel injection in synchronization with the rotation of the engine, and the amplifier 29 thereby amplifies the voltage applied from the piezoelectric actuator power supply 30 to the piezoelectric actuator element 21. Add. This causes the piezoelectric actuator element 21 to extend and push the piston 22 . The pressure rises from the fuel passage 23, and this pressure is transmitted to the nozzle tip 10 through the check valve 24 and acts on the needle valve 12. When this pressure overcomes the mounting force of the nozzle spring 13, the needle valve 12 is pushed up and the fuel is ejected from the nozzle 11 through the valve seat. Since the amount of movement of the piezoelectric actuator element is determined by the applied voltage, the amount of fuel ejected is also determined. This injection of fuel becomes a so-called pilot injection.

When the voltage applied to the piezoelectric actuator 21 is removed, the piezoelectric actuator element returns to its original position and pulls the piston 22, so that the pressure in the fuel passage 23 decreases and the fuel from the fuel supply pump 32 flows through the check valve. 31 is opened and the fuel is supplied to the chamber at the tip of the piston 22 through the fuel passage 23. The check valve 31 stops the backflow of fuel by the piston 22. The check valve 24 prevents the fuel flowing in from the fuel passage 16 from flowing backward. Subsequently, main injection of fuel is performed as follows under the control of the controller 19. The tappet 17 is pushed by a cam driven in synchronization with the rotation of a crankshaft (not shown), a push rod (not shown), and a rocker arm (not shown), thereby moving the plunger 1 forward.

While the plunger 1 is moving forward, the controller 19
After the signal to the piezoelectric actuator element 21,
The solenoid 4 is energized by the drive unit 20 in response to a signal from the controller 19, and the poppet valve 3 is pulled toward the valve stem to be seated and close the fuel passage 6. As a result, the plunger chamber 9 is sealed and the internal pressure rises, and the fuel pressure is transmitted to the nozzle tip 10 through the fuel passage 16 and acts on the tip of the needle valve 12, and when this pressure overcomes the mounting force of the nozzle spring 13, The fuel pushes up the needle valve 12 and is ejected from the nozzle 11.

While the plunger 1 is moving forward, the controller 19
When the current from the drive unit 20 to the solenoid 4 is cut off by the signal, the force to pull the poppet valve 3 disappears, and the poppet valve 3 is separated from the valve seat by the force of the return spring 5.
Since the fuel passage 6 communicates with a fuel tank (not shown) via the valve head chamber 34 and the fuel passage 7, and the pressure in the plunger chamber 9 decreases, the pressure at the tip of the needle valve 12 also decreases.
3 prevails, the needle valve 12 is seated, and fuel injection stops. Thereafter, the fuel that is pushed away by the plunger 1 passes through the fuel passage 6, the valve head chamber 34, and the fuel passage 7, and is discharged to a fuel tank (not shown). The interval between the action of the needle valve 1 and the injection pressure with respect to the crank angle according to the action of the above embodiment is shown in Fig. 2(b).
) as shown in the diagram.

[0020]

[Effects of the Invention] Since the present invention provides a pilot injection system as a system independent from the main injection, it is possible to realize injection characteristics suitable for each of the main injection and pilot injection. Therefore, the pilot injection can be performed in a small amount, and the main injection can achieve high-performance injection with high pressure and high injection rate, and the interval between the pilot injection and the main injection can be adjusted appropriately according to the ignitability of the fuel, engine rotation speed, etc. can do. As a result, a high-performance diesel engine with low fuel consumption, low smoke emissions, and low noise can be realized. Furthermore, even with low cetane number fuel, smooth combustion without diesel knocking can be achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view and an overall system diagram of a unit injector according to an embodiment of the present invention. (Indicates the poppet valve is closed.)

FIG. 2 is an injection characteristic diagram. (a) is an injection characteristic diagram of a conventional fuel injection system, and (b) is an injection characteristic diagram of an embodiment of the present invention.

FIG. 3 is a sectional view and a full system diagram of a unit injector of the prior art. (Indicates the poppet valve is closed.)

[Explanation of symbols]

1 Plunger 2 Fuel injection pump body 10 Nozzle tip 12 Needle valve 16 Fuel passage 19 Controller 21 Piezoelectric actuator element 22 Piston 24 Check valve 26 Fuel passage 27 Check valve 23 Fuel passage 35 Fuel reservoir

Claims (1)

[Claims] 1. A fuel injection device for a diesel engine, comprising: a fuel oil passageway (26) communicating with a fuel reservoir (35) of a nozzle adjacent to a seat part of a needle valve (12); and a part of the fuel oil passageway. a piston (22) provided on the piston, and a piezoelectric actuator (22) provided on the rear of the piston.
1), a check valve (24) provided in the fuel oil passage that allows flow only from the piston to the nozzle, a power supply device that drives the piezoelectric actuator, and an engine crankshaft that supplies power to the piezoelectric actuator. A control device that performs main fuel injection and pilot injection in synchronization with the rotation of
19); and a check valve (27) provided in a main injection fuel passage (16) to prevent backflow of fuel.