JPH0461189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel injection device used in a diesel engine.

Diesel engines use fuel injection to
Normally, it is equipped with an injection pump that increases the pressure of the fuel, a fuel injection pipe that supplies the fuel pumped from the injection pump to the nozzle, and a nozzle that injects the high-pressure fuel. There is an injector. This unit injector eliminates the need for a long fuel injection tube, so the injection delay is small, and the volume to be compressed is reduced by the lack of a fuel injection tube, resulting in high injection pressure and atomization of the fuel. In addition to advantages such as good fuel efficiency, it also has other advantages such as being able to increase the injection rate and reducing the amount of fuel left behind at the end of injection.

A fuel injection system in which such a unit injector is disposed in each cylinder has been proposed, for example, in Japanese Patent Application Laid-Open No. 54-50726 (US Pat. No. 412,953), and is shown in FIGS. 1 and 2.

1 and 2, a plunger 4a is slidably inserted into a cylinder 3 bored in the main body 2 of the unit injector 1, and the plunger 4a is connected to a plunger 4b. The plunger 4b is biased upward in the figure by a spring 6 interposed between its head and the main body 2, and a cam (not shown) that rotates in synchronization with the engine is attached to the head upward. Since the plunger 4b is pressed down every rotation of the cam, the plunger 4a connected to the plunger 4b reciprocates up and down.

The pressure chamber 7 of the cylinder 3, which is formed facing one end of the plunger 4a, communicates with a fuel tank (not shown) via fuel supply passages 8a, 8b, and a low-pressure fuel supply pump ( (not shown) supplies fuel in the fuel tank to the pressure chamber 7.

A nozzle 10 is formed in the lower part of the main body 2 to inject fuel in the pressure chamber 7 pressurized by the descent of the plunger 4a into a combustion chamber (not shown). Specifically, the nozzle 10 includes a needle chamber 11, a needle valve 12, a spring 13, a nozzle hole 14, a spring guide 15, and a spring chamber 16, which communicate with the pressure chamber 7 via a fuel passage 9.
Normally, the spring 13 urges the needle valve 12 downward via the spring guide 15 to close the nozzle hole 14, but the fuel in the pressure chamber 7 is sent to the needle chamber 11 via the fuel passage 9, and this When the fuel pressure in the needle chamber 11 overcomes the spring 13,
The needle valve 12 is urged upward to open the nozzle hole 14, and the fuel in the needle chamber 11 is injected from the nozzle hole 14. Therefore, spring 1
3 sets the valve opening pressure of the nozzle 10.

A solenoid valve 18 as a valve device is interposed in the fuel supply passages 8a and 8b communicating with the pressure chamber 7. In the solenoid valve 18, a valve body 21 that slides on a cylinder 20 bored in a valve holder 19 is biased by a spring 22 to open the solenoid valve 18. When a driving current is applied to the solenoid 24, the solenoid 24 By electromagnetic force, the armature 26 urges the valve body 21 in the valve closing direction against the spring 22 to seat it.

When the solenoid valve 18 is opened, the fuel in the pressure chamber 7, which becomes high pressure due to the descent of the plunger 4a, flows through the solenoid valve 18.
The orifice 17 regulates the fuel flow rate at this time, thereby keeping the fuel pressure in the pressure chamber 7 and the passages 8b and 9 at a predetermined value lower than the opening pressure of the nozzle 10. That's what I do.

A control circuit (not shown) that controls the drive current to the solenoid valve 18 includes means for detecting the operating state of the engine (for example, an engine rotation speed sensor, an accelerator sensor that detects the depression angle of the accelerator pedal, and a sensor that detects the cooling water temperature of the engine). Based on the detection signal from the water temperature sensor, crank angle sensor that detects the crank angle, etc.
A signal having a drive pulse width optimal for the engine operating condition is output to the solenoid 24 to control the opening and closing of the solenoid valve 18.

A fuel relief passage 28 communicating with the spring chamber 16
After merging, the fuel relief passage 28b communicating with the annular groove 29 formed in the upper part of the cylinder communicates with the fuel supply passage 8a upstream of the solenoid valve 18, and returns excess fuel to the passage 8a.

Therefore, the fuel in the fuel tank pre-pressurized by the fuel supply pump is transferred from the fuel supply passage 8a to the solenoid valve 1.
When the fuel is supplied to the pressure chamber 7 via the valve 8 (open), the plunger 4a is lowered by a cam that rotates in synchronization with the engine and begins to pressurize the fuel in the pressure chamber 7. At this point, however, the electromagnetic Since the valve 18 is open, a part of the pressurized fuel escapes through the solenoid valve 18, and the fuel flow rate is regulated by the orifice 17, so that the fuel pressure in the pressure chamber 7 and passages 8a and 9 does not exceed a predetermined value. Not reached.

When the solenoid 24 is energized and the electromagnetic valve 18 is closed during the descent of the plunger 4a, the fuel in the pressure chamber 7 is trapped and the fuel pressure increases, and this fuel pressure reaches the needle chamber 11 via the fuel passage 9. When the fuel pressure in the needle chamber 11 overcomes the downward urging force of the spring 13 (valve opening pressure of the nozzle 10), the needle valve 12 is pushed upward and the nozzle hole 14 is opened.
Fuel in the needle chamber 11 is injected into a combustion chamber (not shown).

When the solenoid 24 is de-energized at a predetermined crank angle and the solenoid valve 18 is opened, part of the fuel in the pressure chamber 7 escapes to the fuel supply passage 8a via the solenoid valve 18 as described above, so that the needle chamber The fuel pressure at No. 11 quickly decreases to below the opening pressure of the nozzle 10, and the injection ends.

In other words, fuel injection is performed while the solenoid valve 18 is closed.
By changing the timing and duration of energization of the solenoid 24, which opens and closes, depending on the operating condition, the injection timing and amount of fuel injected from the nozzle 10 can be optimally controlled.

By the way, in such a fuel injection device,
It is considered that the solenoid valve 18 is opened and closed twice per fuel injection stroke, and for example, as shown in FIG. 3, some fuel is injected immediately before the main injection.

This is so-called pilot injection, and in this case, main injection A, where most of the fuel is injected, is set to occur near compression top dead center of the engine, and pilot injection B is determined to be performed before top dead center, taking into account the ignition delay. .

According to this, combustion is performed by pilot injection prior to combustion by main injection, and a good combustion condition is obtained, and combustion does not occur suddenly at one time, so especially in the low engine speed range. This reduces the combustion peak pressure of the engine, reduces noise, reduces NOx in the exhaust, and improves fuel efficiency and smoke.

However, in order to carry out such pilot injection, the electromagnetic valve 18 is required to have extremely high responsiveness. For example, the fuel injection period is several milliseconds during normal operation, and the solenoid valve 18 must be opened and closed twice during this period, and the opening and closing period is even shorter during low-load operation with a small injection amount. It will become.

For this reason, while the solenoid valve 18 becomes larger, there is a problem that the durability of the solenoid valve 18 may be deteriorated and its operation may become unstable. There was also the problem that control became difficult.

The object of the present invention is to provide a fuel injection device that makes use of the fact that the closing pressure of the nozzle is lower than the opening pressure of the nozzle and allows pilot injection to be performed without opening and closing a solenoid valve twice during one injection stroke. There is.

To this end, the present invention provides a plunger that reciprocates in synchronization with the engine, a pressure chamber formed facing one end of the plunger, a nozzle that communicates with the pressure chamber and opens at a predetermined pressure or higher, and a nozzle that communicates with the pressure chamber. In a fuel injection device equipped with a solenoid valve device that is interposed in a fuel supply passage and releases high-pressure fuel depending on the operating state of the engine, a pressure that is approximately the same as the valve opening pressure of the nozzle is maintained between the nozzle and the solenoid valve device. Valve means is provided which opens to release a portion of the high-pressure fuel and then switches to the closed side in response to the released high-pressure fuel. Further, a control device is provided which biases the valve means in the initial position direction, that is, in the direction of closing the fuel supply passage against the high pressure from the plunger pressure chamber, with a force that increases as the engine speed increases.

That is, when the pressure of the fuel pumped from the plunger exceeds the valve opening pressure of the nozzle, the nozzle opens and begins to inject high-pressure fuel, but almost at the same time, the valve means is opened to release a portion of the high-pressure fuel. , reduce the pressure of the fuel below the nozzle closing pressure, and then close the nozzle. Then, by using this released high-pressure fuel, the valve means is switched to the closed side, thereby increasing the pressure of the fuel and opening the nozzle again.

This allows pilot injection and main injection to be performed by opening and closing the solenoid valve device once during one injection period,
At this time, the timing from pilot injection to main injection is appropriately controlled by adjusting the switching speed of the valve means in accordance with the engine speed.

Embodiments of the present invention will be described below based on the drawings.

FIG. 4 is a cross-sectional view of the structure of an embodiment of the present invention, in which 31 is a plunger of a unit injector 30 that reciprocates within a cylinder 32 by a cam (not shown) that rotates in synchronization with the engine; A fuel supply passage that leads fuel from the fuel pump 35 to the pressure chamber 34 of the pressure chamber 34;
This is a fuel passage that sends the pressurized fuel to the needle chamber 39 of the needle valve 38 of the nozzle 37.

In the middle of the fuel supply passage 33, there is an accelerator sensor 40 and a rotation sensor 4 that detect the operating state of the engine.
1. A solenoid valve 44 is installed to open and close the passage 33 in response to commands from a control circuit 43 based on signals from the water temperature sensor 42 and the like.

The solenoid valve 44 is controlled to close only at a predetermined time during the compression process of the plunger 31,
During this valve closing period, the fuel in the pressure chamber 34 is pressurized by the plunger 31.

Further, the nozzle 37 is arranged so that the pressure of the fuel fed from the pressure chamber 34 to the needle chamber 39 is applied to the spring 4.
When the spring force of 5 exceeds the opening pressure of the nozzle 37, the needle valve 38 is lifted and opened, and the high-pressure fuel is injected from the injection hole 46.

After this injection, when the fuel pressure decreases, the needle valve 38 descends and the nozzle 37 closes, but at this time, the pressure of the injected fuel is also applied to the tip (seat surface) of the needle valve 38. Nozzle 37 closes at a pressure somewhat lower than the opening pressure.

That is, once the nozzle 37 is opened, fuel continues to be injected until the pressure of the nozzle 37 drops to a closing pressure that is lower than the opening pressure of the nozzle 37.

Then, by utilizing the difference between the valve opening pressure and the valve closing pressure of the nozzle 37, the fuel supply passage 38 between the solenoid valve 44 and the nozzle 37 is opened at approximately the same pressure as the valve opening pressure of the nozzle 37. While letting some of the high-pressure fuel escape,
A valve means 47 is provided which is then switched to the closed side in response to the released high pressure fuel.

As shown in FIG. 5, this valve means 47 includes a valve sleeve 52 having a high pressure port 48 connected to the fuel supply passage 33 and a return port 51 connected to the fuel tank 50 via an action chamber 49;
It is slidably housed in this valve sleeve 52,
It is composed of a valve body 53 that selectively opens, closes, and communicates the high pressure port 48 and the return port 51.
A return spring 56 is interposed for biasing the high-pressure port 48 toward the initial position where it is seated on the high-pressure port 48 side.

Specifically, the action chamber 49 of the valve sleeve 52
The opening 57 of the high pressure port 48 and the opening 58 of the return port 51 are formed to form a tapered seat surface, and the head of the valve body 53 that slides within the action chamber 49 corresponds to this. Part 59
is formed into a symmetrical conical shape, and the return spring 5
The high-pressure port 48 is closed when the valve body 53 is at its most forward position (the position shown in the figure) due to the biasing force No. 6, and the return port 51 is closed at its last position (the rightmost position in the figure).

The spring force of the return spring 56 is such that when the fuel pressure applied to the high pressure port 48 becomes approximately equal to the valve opening pressure of the nozzle 37 described above, the valve body 53 begins to retreat and the high pressure port 48 is opened. Set.

Further, this valve body 53 is set to have a short stroke (for example, several mm) so that both ports 48 and 51 can be opened and closed quickly by its movement.

The valve body head 59 partitions the action chamber 49 into front and rear parts, and a relief hole 62 is formed in the valve body head 59 to communicate the front chamber 60 and the rear chamber 61, and the relief hole 62 has a predetermined diameter. An orifice 63 is provided.

That is, when the pressure of the fuel sent to the high pressure port 48 becomes approximately equal to the valve opening pressure of the nozzle 37, the high pressure port 48 opens and high pressure fuel flows into the front chamber 60 of the valve body 53. A portion of this inflowing fuel is gradually returned to the fuel tank 50 from the relief hole 62 through the orifice 63, the rear chamber 61, and the return port 51, whereby the pressure in the front chamber 60 is reduced at a rate determined by the orifice 63. It decreases. At this time, the pressure in the front chamber 60 acts on the front surface of the valve body 53, so that the valve body 53 retreats in parallel with the decrease in pressure, and then the return port 51 is closed.

Therefore, the pressure of the fuel applied to the high-pressure port 48, that is, the pressure of the fuel pumped from the pressure chamber 34 of the plunger 31, increases to the valve-opening pressure of the nosol 37, then drops below the valve-closing pressure, and then returns to the valve-closing pressure. The pressure rises above the valve opening pressure. As a result, plunger 3
In the first compression stroke, the nozzle 37 is opened twice to perform pilot injection and main injection.

On the other hand, the moving speed (retreating speed) of the valve body 53
changes depending on the flow rate of the fuel pumped from the plunger 31, and the higher the flow rate, the faster the flow rate.For example, the higher the engine speed, the shorter the interval between pilot injection and main injection, making it difficult to maintain an appropriate value. Difficult to maintain.

Therefore, in order to adjust the moving speed of the valve body 53 regardless of the flow rate, a control means is provided that sets the switching time of the valve means 47 according to the operating state of the engine.

Specifically, in the damper chamber 55 behind the valve body 53,
A pressure control valve 64 that introduces fuel (low pressure) from the fuel pump 35 and adjusts the pressure of the fuel.
is provided.

A pressure sensor 65 is installed on the discharge side of the fuel pump 35, and a signal from the pressure sensor 65 is sent to a control circuit 43, which controls the pressure control valve 6 based on the signals from each of the sensors 40 to 41.
Control the set pressure of step 4. In this case, for example, the higher the engine speed, the higher the fuel pressure is controlled. Note that 66 is an orifice and 71 is an accumulator.

Thereby, the resistance force against the backward direction of the valve body 53 is strengthened in accordance with engine rotation, etc., and its moving speed can be changed arbitrarily. Therefore, it is possible to maintain the engine at an appropriate value from pilot injection to main injection in accordance with the operating state of the engine.

With this configuration, the third solenoid valve 44 does not have to be opened and closed twice during one injection stroke as in the conventional example.
Pilot injection can be easily performed as shown in the figure.

For this reason, it is not necessary to use the solenoid valve 44 with such high responsiveness, and it is possible to maintain stable operability of the solenoid valve 44 and improve its durability.

Furthermore, the period from pilot injection to main injection can be accurately controlled according to the operating condition of the engine, so that optimum injection characteristics suitable for the operating condition can be obtained.

As a result, the fuel condition of the engine is always maintained in the best condition, and engine performance can be significantly improved.
In particular, it is possible to reduce noise in the low engine speed range and NOx in the exhaust gas, and to improve fuel efficiency.

The period from the pilot injection to the end of the main injection and its timing correspond to the valve closing period and valve closing timing of the solenoid valve 44, and the period of the pilot injection corresponds to the valve closing period and the valve closing timing of the solenoid valve 44. It is determined by the diameter of the orifice 63. Therefore, the injection amounts of the pilot injection and the main injection can be set and controlled by the diameter of the orifice 63 and the closing period of the solenoid valve 44, respectively.

FIG. 6 shows another embodiment of the present invention, in which when the fuel pressure from the fuel pump 35 is applied to the damper 55 of the valve means 47, the valve opening pressure of the valve body 53 (high pressure port 48 This prevents the opening pressure from changing.

Specifically, a push rod 67 is integrally attached to the rear of the shaft portion 54 of the valve body 53, and the return spring 6 that urges the valve body 53 toward the high pressure port 48 is engaged with the push rod 67. A piston 68 that slides in the damper chamber 55 is also fitted between the push rod 67 and the valve body 53 so as to be freely slidable, and between the piston 68, the push rod 67, and the valve body 53. A small gap (play) 69, 70 is provided in the axial direction. The gaps 69 and 70 are between the valve body 53 and the piston 68.
are each set to predetermined dimensions at the illustrated positions.

Therefore, when the valve body 53 starts to open,
The fuel pressure in the damper chamber 55 does not act on the valve body 53, but acts after the valve body 53 contacts the piston 68.

Thereby, regardless of the fuel pressure in the damper chamber 55, the valve opening pressure of the valve body 53 can always be kept constant (determined only by the spring force of the return spring 56), that is, stable pilot injection can be performed.

As explained above, according to the present invention, it is possible to perform optimal pilot injection according to the operating condition of the engine without opening and closing the solenoid valve device twice during one injection stroke, improving the controllability and reliability of the device. This has the effect that the engine performance, particularly in the low rotation range, can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional unit injector, Fig. 2 is a partial sectional view thereof, Fig. 3 is a characteristic diagram showing pilot injection and main injection, and Fig. 4 is a structural sectional view showing an embodiment of the present invention. FIG. 5 is a detailed sectional view of the main part thereof, and FIG. 6 is a detailed sectional view of the main part showing another embodiment of the present invention. 30...Unit injector, 31...Plunger, 32...Cylinder, 33...Fuel supply passage, 34
...pressure chamber, 35...fuel pump, 36...fuel passage,
37... Nozzle, 38... Needle valve, 39... Needle chamber, 40... Accelerator sensor, 41... Rotation sensor, 42... Water temperature sensor, 43... Control circuit, 44
... Solenoid valve, 47... Valve means, 49... Action chamber, 53...
Valve body, 55... Damper chamber, 56... Return spring, 62... Relief hole, 63... Orifice, 64...
Pressure control valve, 65...Pressure sensor, 67...Push rod, 68...Piston, 69, 70...Gap.

Claims (1)

[Claims] 1. A plunger that reciprocates in synchronization with the engine, a pressure chamber formed facing one end of the plunger, a nozzle that communicates with the pressure chamber and opens at a predetermined pressure or higher, and a fuel supply passage that communicates with the pressure chamber. In a fuel injection device equipped with an interposed electromagnetic valve device that releases high-pressure fuel according to the operating state of the engine, the high-pressure fuel is opened between the nozzle and the electromagnetic valve device at approximately the same pressure as the opening pressure of the nozzle. The valve means is then switched to the closed side in response to the released high-pressure fuel, and the valve means is urged toward the initial position by a force that increases as the engine speed increases. A fuel injection device characterized in that it is provided with a control means.