JPH0610788A - Fuel injection device - Google Patents

Abstract

PURPOSE:To stabilize injection rate in pilot injection timing in a fuel injection device having a two-stage lift regulating mechanism. CONSTITUTION:A needle valve 5 is lifted by fuel pressure force fed from a plunger barrel 2 through a high pressure path 19. In pilot injection, first stage lift is regulated in a position of a first rod 14 abutting against a second rod 25. When a spill valve 26 is opened, the needle valve 5 is once lowered and then high pressure fuel acts on a back pressure chamber 18 through a branch path 21. A force of a second spring 28 is cancelled or reduced by the high pressure, and in the main injection the lift is not regulated even if the first rod 14 abuts against the second rod 25. When the needle valve 5 is lifted until the second rod 25 abuts against a stopper 31a, the lift regulation of the main injection is carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device, and more particularly, it uses a two-stage fuel injection system consisting of a pilot injection period and a main injection period to optimize the fuel injection rate during the ignition period to generate engine noise and vibration. The present invention relates to a fuel injection device for a diesel engine, which is capable of reducing NOx and NOx in exhaust gas.

[0002]

2. Description of the Related Art In a diesel engine, there is a period called ignition delay time from fuel injection to ignition. The fuel injected during this period burns all at once due to ignition, causing the pressure inside the combustion chamber to rise rapidly, producing a sound called a diesel knock, which is peculiar to a diesel engine. Further, if the fuel burns all at once, the pressure in the combustion chamber becomes higher than necessary, and the combustion temperature also rises, which becomes a factor to increase the NOx emission amount. The above-mentioned problems such as diesel knock and increase in NOx are more likely to occur as more fuel is injected during the ignition delay period.

In order to solve the above-mentioned problems, a fuel injection device has been proposed which aims to reduce the amount of fuel injected during the ignition delay period to alleviate rapid combustion (Japanese Patent Laid-Open No. 62-62-62). 13740).

The above conventional fuel injection device will be described with reference to FIG. In the figure, the fuel supplied from the fuel tank by a fuel pump (not shown) flows into the injection nozzle 20 through the pipe 7. The fuel pipe 7 is branched on the way, and the branched pipe portion 8 is connected to an accumulator 9. The strength of the compression spring 12 that biases the piston 11 that is slidably accommodated in the accumulator 9 is the same as that of the compression spring 23b that biases the needle valve 23 that is accommodated in the injection nozzle 20 downward in the figure. It is set slightly higher than the strength. The fuel flowing into the injection nozzle 20 is configured to reach the pressure receiving chamber 30 from the valve chamber 29 through the groove 32a provided in the partition 32 of the needle valve 23.

In the injector configured as described above, when fuel is supplied to the injection nozzle 20, the pressure receiving chamber 30
Pressure gradually rises. When this pressure reaches the valve opening pressure, the needle valve 23 rises over the spring 23b,
The tip of the needle valve 23 separates from the valve seat surface 33 and the injection port 2
Fuel is ejected from 2.

Since the fuel is continuously pumped even after the injection of fuel is started, the pressure in the pipe 8 rises. When this pressure exceeds the strength of the spring 12 of the accumulator 9, the piston 11 rises. At this moment, the pressure receiving chamber 30
The pressure is decreased, the needle valve 23 is pushed down by the spring 23b, and the ejection of fuel is stopped. The period up to this point is the pilot injection period or the pre-injection period in which the injection rate is kept low.

The piston 11 is fed by the subsequent pressure feeding of fuel.
Further rises, and the piston 11 stops rising when its top comes into contact with the stopper 16. If the fuel is further pumped in this state, the pressure in the pressure receiving chamber 30 rises again, the needle valve 23 rises, and the fuel is ejected. The main injection period starts from this time. During the main injection period, the piston 11 is already at the upper limit, so the volume of the pipe 8 does not increase, and fuel injection with an increased injection rate is performed by the pumping operation of the fuel pump.

Further, Japanese Laid-Open Patent Publication No. 2-267363 proposes the following fuel injection device capable of pilot injection. In this fuel injection device, a back pressure chamber is provided behind the needle valve, that is, on the side opposite to the direction of the fuel injection port. Then, the fuel supplied from the fuel pump acts on the pressure receiving surface of the needle valve to generate a pressure for raising the needle valve. On the other hand, fuel is also supplied to the back pressure chamber, and the pressure of the fuel urges the needle valve in the valve opening direction.

An electromagnetic opening / closing valve is provided in the fuel supply passage to the back pressure chamber, and the electromagnetic opening / closing valve is opened / closed at a predetermined timing to control the supply of fuel to the back pressure chamber. When the electromagnetic opening / closing valve is opened during the fuel injection to supply the fuel to the back pressure chamber, the needle valve is lowered by the pressure of the fuel to open. That is, the pilot injection period is determined by the opening / closing timing of this electromagnetic opening / closing valve.

The fuel injection devices described in the above two publications have a one-stage lift control mechanism, and the upper limit value of the lift amount of the needle valve is the same in both pilot injection and main injection.

On the other hand, there is also a fuel injection device having a two-stage lift restriction mechanism in which the upper limit value of the lift amount is changed between pilot injection and main injection. In the fuel injection device of the two-stage lift regulation mechanism, for example, the spring 23b in FIG.
The urging means corresponding to is composed of two springs having different strengths, the first spring having a small strength is first pushed up to open the needle valve at the time of pilot injection, and at the time of the main injection, the first spring and a stronger spring than this. The second spring having a large thickness is pushed up to open the needle valve. Thereby, the injection amount at the time of pilot injection can be reduced.

[0012]

However, the conventional fuel injection device has the following problems. First, in the fuel injection device of the one-stage lift regulation mechanism, the lift amount is not constant depending on the size of the load and the engine rotation range. In particular, in a low load or low rotation range, the needle valve may not rise to a predetermined value, and fuel may be injected with a halfway lift amount. In the pilot injection method, one of the important points to consider is how to accurately inject a small amount (5 to 10% of the total injection amount) of fuel during pilot injection. However, if the lift amount is not constant as described above, there arises a problem that the purpose of pilot injection of accurately injecting a small amount of fuel cannot be achieved.

Further, during the main injection period in the fuel injection device of the two-stage lift regulation mechanism, it is desirable to raise the needle valve at once and inject a required amount of fuel in a relatively short period. Nevertheless, even in the main injection, the operation of the two-stage lift regulation mechanism is started by first pushing up the first spring, as in the pilot injection. Then, when the first spring is pushed up, the rise of the needle valve is temporarily stopped, and then the second spring is further pushed up to raise the needle valve, so that the final fuel injection is performed. The injection also becomes a two-step operation.
As a result, it is difficult to inject a required amount of fuel at a time at the optimum injection timing to improve the combustion efficiency, and there is a problem that smoke is often generated.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a fuel injection device capable of performing accurate fuel injection at the time of pilot injection and at the same time injecting a required amount of fuel at the time of main injection.

[0015]

[Means for Solving the Problems] The above problems are solved.
Therefore, the present invention is provided in a valve chamber so as to be reciprocally movable.
By the first spring through the first push rod
The needle valve urged in the valve closing direction and the first pusher
Attached to the back pressure chamber at the rear of the rod with a second spring.
Is provided so as to project into the back pressure chamber,
Limit the lift amount of the first push rod to the first planned amount
The second push rod for
From the high pressure passage for supplying pressurized fuel and the high pressure passage
A branch passage that branches to the back pressure chamber, and
It is installed on the way, and the pressure in the high pressure passage exceeds the planned value.
And the expected timing drive signal was supplied
A valve that opens the branch passage at any time
The point is that it was done.

[0016]

In the present invention having the above characteristics, when the fuel supply pressure rises, the pressure in the high pressure passage increases, and when the pressure reaches the first spring, the needle valve rises. When the first push rod comes into contact with the second push rod, the rise of the needle valve is once stopped by the force of the second spring acting on the second push rod. afterwards,
The valve in the branch passage is opened when the pressure in the high-pressure passage exceeds a predetermined value or when a predetermined timing drive signal is supplied. As a result, the pressure in the high-pressure passage drops momentarily, and the needle valve descends and closes. The above is the pilot injection period.

In the main injection period following the pilot injection period, when the fuel supply pressure rises, the pressure in the high pressure passage again increases. At this point, however, since the branch passage is open, the back pressure chamber is opened via this branch passage. High-pressure fuel is supplied to.
This fuel pressure acts in the direction of pushing up the second push rod, that is, in the direction of lifting the needle valve. The fuel pressure in the back pressure chamber that acts on the second push rod acts so as to cancel the force of the second spring that biases the second push rod in the anti-lift direction.

As a result, during the main injection period, even if the first push rod comes into contact with the second push rod, the rise of the needle valve does not stop at that time. The rise of the needle valve is caused by hitting a predetermined rise regulating surface such as the upper wall surface of the valve chamber accommodating the needle valve or the upper wall surface of the spring chamber accommodating the second spring by the second push rod. The ascent stops at the point of contact.

Thus, during the pilot injection, fuel is injected by the lift amount from when the needle valve starts opening the valve until the first push rod contacts the second push rod, and during the main injection, the valve is opened. After that, the fuel is injected with the lift amount up to the rising regulation surface. That is, different lift amounts are set for the pilot injection and the main injection.

Further, during the main injection period, the force of the second spring is canceled or reduced, so that the rising does not pause for a while, and the maximum lift amount increases at a stretch.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of a fuel injection device (hereinafter referred to as an injector) showing an embodiment of the present invention.

In the figure, a valve chamber 4 is provided at the tip of the injector body 1, and a needle valve 5 is housed inside the valve chamber 4. A fuel injection port 6 is provided on the valve seat surface 10 at the tip of the valve chamber 4, and is opened and closed by the movement of the needle valve 5.

Behind the needle valve 5 is a first spring chamber 17
The first spring chamber 17 is provided with a first compression spring (hereinafter referred to as the first spring) 15 and a first push rod having a step for receiving the repulsive force of the first spring 15 (hereinafter referred to as the first push rod). 14 is stored. The first rod 14 is provided so as to penetrate the first spring chamber 17, and one end thereof is brought into contact with the rear end surface of the needle valve 5. Therefore, the first spring 15 is connected to the first rod 1
It is compressed by the step surface of 4 and the wall surface of the first spring chamber 17, and the repulsive force is transmitted to the needle valve 5 via the first rod 14. A back pressure chamber 18 is provided adjacent to the other end of the first rod 14, that is, the rear end. An end portion of a second push rod (hereinafter referred to as a second rod) 25 projects into the back pressure chamber 18 and the first rod 1
Opposite 4 The second rod 25 is urged downward by a second compression spring (hereinafter referred to as a second spring) 28, that is, in the valve closing direction of the needle valve 5. Before the operation of the injector, that is, in the initial state, the first rod 14
The second rod 25 is set to face each other with a distance L1. This interval L1 is the lift amount at the time of pilot injection.

Second spring chamber 3 for accommodating the second spring 28
1 is provided with a stopper 31a for defining the rising limit of the second rod 25, that is, the maximum lift amount of the needle valve 5. In the initial state, a gap L2 is provided between the stopper 31a and the second rod 25. That is, the sum of the distance L2 between the stopper 31a and the second rod 25 and the distance L1 is the maximum lift amount of the needle valve 5.

From the fuel tank (not shown) to the fuel supply passage 1
The fuel supplied via 3 is received in the plunger barrel 2 bored in the upper portion of the injector body 1. The plunger 3 housed in the plunger barrel 2 is engaged at one end with a cam (not shown) that rotates in synchronization with the engine, and moves vertically in the drawing in the plunger barrel 2 in synchronization with the engine. Reciprocates.

A fuel escape groove 3a for controlling the fuel injection amount is provided on the circumferential surface of the plunger 3. For example, depending on the required fuel injection amount, the plunger 3 is rotated by a predetermined amount by a rotating means (not shown), and the position of the plunger 3 in the rotating direction with respect to the fuel supply passage 13 is adjusted. By doing so, even if the stroke length of the reciprocating motion of the plunger 3 is constant, the plunger 3 descends according to the position of the plunger 3 in the rotation direction, and the escape groove 3a and the fuel supply passage 13 are connected. The timing of connection is different.

That is, the escape groove 3a and the fuel supply passage 13
When is connected, the pressure in the plunger barrel 2 drops to the fuel supply pressure from the fuel tank. As a result, the pressure in the valve chamber 4 also decreases, the needle valve 5 descends, and the injection port 6 is closed. The closing timing changes depending on the position of the plunger in the rotation direction, and the amount of fuel corresponding to the closing timing is injected.

A high pressure passage 19 communicates between the plunger 2 and the valve chamber 4, and a branch passage 21 is provided in the middle of the high pressure passage 19. The branch passage 21 extends to the plunger barrel 2 and the back pressure chamber 18 via a decompression chamber 24 provided on the way. The decompression chamber 24 is provided with a spill valve 26, and the branch passage 21 is opened and closed by moving the spill valve 26 forward and backward with respect to the decompression chamber 24. The spill valve 26 is biased in the closing direction of the branch passage 21 by a third compression spring 27.

In the above structure, the loads on the first spring 15 and the second spring 28 are set to satisfy the following equation. In the following equation, F1 is the load of the first spring 15, F2 is the repulsive force of the second spring 28, P0 is the supply pressure (feed pressure) of the fuel supplied from the fuel tank, and P1 is before the opening of the spill valve 26, that is, The maximum injection pressure at the time of pilot injection, P2 is the valve opening pressure at the time of main injection, Sn is the pressure receiving area of the needle valve, and Sa is the pressure receiving area of the second rod 25. F2> (P1 × Sn) −F1 + (P0 × Sa) (Equation 1) F2 <Sa × P2 (Equation 2) Next, the operation of the injector in this embodiment will be described with reference to the timing chart of FIG. Explain. 2A shows a fuel pressure waveform, FIG. 2B shows an injection rate waveform, FIG. 2C shows a needle valve lift amount waveform, and FIG. 2D shows a spill valve lift amount waveform. Is.

First, the fuel introduced into the plunger barrel 2 passes through the high pressure passage 19 and the valve chamber 4 and the branch passage 21.
And also to the back pressure chamber 18 via the port 34 of the plunger barrel 2.

Then, as the plunger 3 descends,
First, the port 34 connected to the fuel supply passage 13 and the branch passage 21 is closed. Therefore, in this state, the first
The feed pressure P0 is applied to the rod 25 (pressure receiving area Sa).

When the plunger 3 further descends, the fuel pressure in the valve chamber 4 rises, and when the force pushing up the needle valve 5 exceeds the load F1 of the first spring 15 by this pressure, the needle valve 5 starts to rise. Then, fuel injection from the injection port 6 is started (timing T0).

By the way, as in the above-mentioned formula 1, the load of the second spring 28 increases the needle valve 5 (pressure receiving area Sn) by the maximum injection pressure P1 at the time of pilot injection to the second rod 25 (pressure receiving area Sa). ) Is added by the feed pressure P0, and is set to be larger than the force obtained by subtracting the load of the first spring 15. Therefore, the needle valve 5 is stopped at the position where the first rod 14 is in contact with the second rod 25, that is, when the needle injection amount is increased by the pilot injection lift amount L1.

When the plunger 3 is further lowered to increase the fuel pressure and the pressure reaches the opening pressure of the spill valve 26, the spill valve 26 starts to rise (timing T).
1).

At the same time when the spill valve 26 starts to rise, the branch passage 21 opens and the pressure in the valve chamber 4 drops, so that the needle valve 5
Goes down. At timing T3, the needle valve 5 finishes descending, the injection port 6 is closed, and fuel injection is also temporarily stopped. Once the spill valve 26 is raised, the spill valve 26 is kept in the raised state by the fuel pressure in the branch passage 21 even after the pilot injection is completed. When the spill valve 26 rises, the high-pressure fuel also flows into the back pressure chamber 18 side, and the same pressure as the fuel pressure that pushes up the needle valve 5 acts on the second rod 25.

From this state, the plunger 3 further descends, the pressure in the valve chamber 4 rises again, and at timing T4 when the pressure reaches P2, the needle valve 5 rises and main injection is started. By the way, since the load F2 of the second spring 28 is set to be smaller than the force for pushing up the second rod 25 (pressure receiving area Sa) by the valve opening pressure P2 at the time of main injection as in the above formula 2, from the timing T4. In the subsequent main injection period, the force for biasing the second rod 25 in the valve closing direction is canceled by the second spring 28.

As a result, the first rod 14 becomes the second rod 2
Even if the needle valve 5 comes into contact with the needle valve 5, the needle valve 5 is not prevented from moving upward, and the needle valve 5 is raised at once by the total lift amount (L1 + L2) until the second rod 25 comes into contact with the stopper 31a.

Fuel is injected under the total lift amount,
When the plunger 3 further descends and the relief groove 3a and the fuel supply passage 13 are connected, the pressure in the valve chamber 4 becomes equal to the fuel supply pressure from the fuel tank, and the needle valve 5 moves to the first position.
It is pushed back by the spring 15 and the fuel injection ends (timing T5).

When the injection of fuel is completed and the plunger 3 rises to open the fuel supply passage 13 and the pressures in the high pressure passage 19, the branch passage 21 and the valve chamber 4 become equal to the feed pressure P0, the spill valve 26 also descends. Then, the initial state is reached (timing T6).

Next, a second embodiment of the present invention will be described. In the second embodiment, a solenoid driven valve is provided instead of the spill valve pressed by the spring. Then, by setting the drive signal supplied to this valve arbitrarily, the injection rate waveform suitable for the purpose can be obtained.

FIG. 3 is a diagram showing a valve provided in the middle of the branch passage. The second embodiment has the same configuration as that of the first embodiment except that a valve that is opened and closed by a solenoid is provided instead of the spill valve 26. In FIG. 3, a valve 35, which is rotatable in the direction of arrow A, is provided in the middle of the branch passage 21 in place of the spill valve 26. The valve 35 has a pinion 36, and the pinion 36 is arranged so as to mesh with a rack 38 which is reciprocally moved by a solenoid 37.
The valve 35 has a vertical groove 39, which is shown in FIG.
At the position of, the branch passage 21 is vertically divided. Then, the valve 35 is rotated and the vertical groove 39 is formed in the branch passage 2
When directed to the 1 side, the branch passages divided by the valve 35 are connected to one [FIG. 3 (b)].

The operation of the second embodiment having the valve 35 constructed as described above is shown in the timing chart of FIG. 4 (a) is a fuel pressure waveform, FIG. 4 (b) is an injection rate waveform,
FIG. 4C is a diagram showing the lift amount waveform of the needle valve, and FIG. 4D is a diagram showing the waveform of the solenoid drive signal.

In FIG. 4, when the plunger 3 descends and the pressure of the fuel in the injector increases, the strength of the first spring 15 pressing the needle valve 5 downward, that is, the valve opening pressure is reached (timing. At T0), the needle valve 5 rises by the lift amount L1 and fuel is ejected.

When the fuel is ejected while the injection rate gradually increases and the current is supplied to the solenoid 37 at the timing T1, the valve 35 is rotated and the branch passage 21 is connected,
Fuel pressure is applied to the back pressure chamber 18. Then, the force of the second spring urging the second rod 25 downward is canceled by the pressure of the fuel flowing into the back pressure chamber 18, and the needle valve 5 causes the second rod 25 to move to the second spring chamber 31. Until it comes into contact with the stopper 31a provided at the end of the, i.e., the lift amount (L1 + L2). As a result, the fuel is injected with the injection rate increasing at a higher rate than before.

Subsequently, when the plunger 3 further descends to connect the escape groove 3a and the fuel supply passage 13, the pressure in the valve chamber 4 becomes equal to the fuel supply pressure (feed pressure) from the fuel tank, and the needle valve 5 Is pushed back by the first spring 15 and the fuel injection ends (timing T3).

When it is desired to continue the state where the fuel injection rate is low at the initial stage of injection for a long time, the timing of current supply to the solenoid 37 may be shifted to the timing T2. As a result of shifting the current supply timing to timing T2, the fuel pressure drop shifts backward and fuel injection ends at timing T4.
As described above, in the second embodiment, by appropriately controlling the drive timing of the solenoid 37, it is possible to obtain the injection rate waveform suitable for the purpose. The drive timing of the solenoid 37 is controlled, for example, to be late in the low rotation range of the engine and early in the high rotation range of the engine.

In the second embodiment, the pressure does not drop sharply even when the valve 35 is opened as in the first embodiment because the branch passage 21 is simply opened and closed by the valve 35. This is because the decompression chamber 24 for increasing the capacity in the middle of 21 is not provided.

In the above description, the maximum lift amount of the needle valve 5 is defined by the position where the stopper 31a and the second rod 25 come into contact with each other, but the present invention is not limited to this.
For example, the stopper 31a may be eliminated or the distance L2 may be made larger to substantially eliminate the function of defining the maximum lift amount (only the function of the second spring 28 as a guide member remains).
Instead, the maximum lift amount can be regulated by adjusting the position where the top of the needle valve 5 contacts the upper wall surface of the valve chamber 4. That is, the dimensions may be set so that the distance L3 becomes the maximum lift amount.

[0049]

As is apparent from the above description, according to the present invention, the following effects can be obtained. Since the second spring acts on the second rod until the branch passage is opened,
A fine lift amount can be set reliably during the pilot injection period. Further, after the branch passage is opened, the urging force of the second spring acting on the second rod is canceled by the fuel pressure supplied to the back pressure chamber, and the second rod or needle valve becomes the maximum lift amount defining surface. The needle valve is raised all at once until it abuts, that is, by the maximum lift amount.

That is, different lift amounts can be set for the pilot injection and the main injection. As a result, a stable injection rate can be obtained during pilot injection regardless of changes in load and rotation range, and during main injection, the required amount of fuel can be injected all at once in a short time, improving combustion efficiency and increasing the amount of smoke generated. Is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a fuel injection device showing a first embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the first embodiment.

FIG. 3 is a cross-sectional view showing the main parts of the second embodiment.

FIG. 4 is a timing chart showing the operation of the second exemplary embodiment of the present invention.

FIG. 5 is a cross-sectional view of a fuel injection device showing a conventional technique.

[Explanation of symbols]

1 ... Injector body, 2 ... Plunger barrel, 3
... plunger, 4 ... valve chamber, 5 ... needle valve,
6 ... Injection port, 14 ... 1st rod, 15 ... 1st spring,
17 ... First spring chamber, 18 ... Back pressure chamber, 19 ... High pressure passage, 21 ... Branch passage, 24 ... Decompression chamber, 25 ... Second
Rod, 26 ... Spill valve, 27 ... Third spring, 28
... second spring, 31 ... second spring chamber, 31a ... stopper

Claims (4)

[Claims] 1. A needle valve that is reciprocally provided in a valve chamber and is urged in a valve closing direction by a first spring via a first push rod; and a needle valve provided behind the first push rod. And a back pressure chamber that is urged by a second spring to project into the back pressure chamber and to face a rear end surface of the first push rod. The lift amount of the first push rod is increased. A second push rod for controlling the amount to a first predetermined amount; a high pressure passage for supplying high pressure fuel to the valve chamber; a branch passage branching from the high pressure passage to reach the back pressure chamber; A valve provided in the middle of the branch passage, which opens the branch passage at any time when the pressure in the high pressure passage exceeds a predetermined value and when a predetermined timing drive signal is supplied, The load on the second spring is Until the valve is opened, it is larger than the force to push up the needle valve, and after the valve is opened, the fuel supplied to the back pressure chamber is smaller than the force to push up the second push rod. A fuel injection device characterized by being set to a value. 2. The valve is biased in a valve closing direction by being pressed by a third spring so that the valve opens when the fuel pressure in the branch passage exceeds the pressing force of the third spring. The fuel injection device according to claim 1, wherein the fuel injection device is a spill valve configured as described above. 3. The fuel injection device according to claim 1, wherein the valve is configured to be driven by a solenoid. 4. The fuel according to claim 3, wherein the timing of opening the valve by driving the solenoid after opening the needle valve is set to be earlier as the engine speed increases. Injection device.