EP0404916A1

EP0404916A1 - Fuel injection nozzle.

Info

Publication number: EP0404916A1
Application number: EP90901717A
Authority: EP
Inventors: Maximilian Kronberger
Original assignee: Voestalpine Metal Forming GmbH
Current assignee: ROBERT BOSCH AG
Priority date: 1989-01-12
Filing date: 1990-01-12
Publication date: 1991-01-02
Anticipated expiration: 2010-01-12
Also published as: DE59008568D1; US5125581A; EP0404917A1; WO1990008257A1; US5125580A; ATE119238T1; JPH03504034A; JPH03504035A; EP0404916B1; WO1990008256A1

Abstract

Un injecteur de carburant, notamment un gicleur de pompe, comprend un pointeau (3) sollicité par un ressort dans le sens de fermeture et une chambre de compression agencée avant le siège du pointeau et en communication avec une chambre d'accumulation (34) délimitée par un piston alternatif (6). L'extrémité du piston alternatif (6) opposée à la chambre d'accumulation (34) reçoit une pression dans une cavité d'amortissement (16) remplissable avec du carburant et comprend un tourillon (17) qui pénètre dans un disque (19) de délimitation de la cavité d'amortissement (16) pourvu d'une ouverture. Le rapport diamètre/hauteur de la partie cylindrique de guidage (7) du piston alternatif (6) est compris entre 1:0,1 et 1:0,4. Le côté du piston alternatif (6) opposé à la chambre d'accumulation (34) comprend un tourillon (17) à section transversale variable qui pénètre dans le disque de délimitation (19) et le côté du piston alternatif (6) qui fait face à la chambre d'accumulation (34) comprend un prolongement de guidage (10) pourvu de rainures (11), ce qui permet d'améliorer la vitesse de réaction et le comportement dynamique de l'injecteur.A fuel injector, in particular a pump nozzle, comprises a needle (3) biased by a spring in the closing direction and a compression chamber arranged before the seat of the needle and in communication with an accumulation chamber (34) delimited by a reciprocating piston (6). The end of the reciprocating piston (6) opposite the accumulation chamber (34) receives pressure in a damping cavity (16) fillable with fuel and comprises a journal (17) which penetrates into a disc (19) delimiting the damping cavity (16) provided with an opening. The diameter/height ratio of the cylindrical guide part (7) of the reciprocating piston (6) is between 1:0.1 and 1:0.4. The side of the reciprocating piston (6) opposite the accumulation chamber (34) comprises a trunnion (17) of variable cross-section which penetrates the boundary disc (19) and the side of the reciprocating piston (6) which faces to the accumulation chamber (34) comprises a guide extension (10) provided with grooves (11), which makes it possible to improve the reaction speed and the dynamic behavior of the injector.

Description

Fuel injector

The invention relates to a fuel injection nozzle, in particular a pump nozzle, with a nozzle needle which is spring-loaded in the closing direction, in which the pressure space in front of the seat of the nozzle needle is connected to a storage space delimited by a spring-loaded evasive piston, the evasive piston on its storage space opposite end is acted upon by the pressure in a fuel-fillable damping space and has a pin which dips into a plate delimiting the damping space and having an opening.

Such a fuel injection nozzle, described in EP-A 277 939, enables the injection process to be subdivided into a pre-injection and a main injection. The very difficult problem of ensuring a favorable injection course under various operating conditions is solved in principle there by damping the movement of the evasive piston, but there are still some inevitabilities.

In a pump nozzle according to the prior art, disturbances in the injection process are observed relatively frequently. Sometimes the evasive piston opens too late, sometimes the pre-injection starts too late and delivers too little, sometimes it stays off completely. It is assumed that these disturbances are caused by statistical fluctuations in the course of the delivery pressure of the pump and the dynamic opening pressure of the valve needle, for example if the valve needle has not yet opened when the dynamic opening pressure of the evasive piston is reached. An increase in this opening pressure would help, but is not possible because the pre-injection would then take too long. This could only be countered by weaker damping of the escape piston. As a result, however, the pre-injection quantity would be too low again at low speed or too high at high speed his. The latter is undesirable for reasons of combustion dynamics and occurs even without increasing the dynamic opening pressure of the evasive piston. At high engine speeds and at full load, the pilot injection changes to the main injection without a break in injection.

Since the volume of the pressure chamber suddenly increases when the nozzle needle is lifted, the injection pressure initially drops at low speed, so that the pre-injection quantity is too low given the low dynamic opening pressure of the evasive piston for the reasons mentioned above.

In order to optimize the combustion process, however, it is desirable that the pre-injection quantities are approximately the same at all speeds and load conditions and the duration of the pre-injection and the injection pause in ° K are approximately the same at all speeds.

These ideal conditions are described as a combustion process in DE-OS 37 35 169, but without any reference to its implementation.

The invention now aims to further develop an injection nozzle of the type mentioned at the outset in such a way that the response speed and the dynamic behavior are improved. In particular, the design according to the invention is intended to ensure that a safe function is maintained by the smallest possible moving mass of the evasive piston and rapid movements. To achieve this object, the design according to the invention essentially consists in that the cylindrical guide part of the evasive piston has a ratio of diameter to height of 1: 0.1 to 0.4, that the evasive piston on its side facing away from the storage space has a pin with a variable cross section has, which dips into the boundary plate, and that the evasive piston on its Storage space facing side has a guide extension with grooves. Due to the fact that the dimensioning of the deflection piston is chosen in a way that deviates from the known designs in such a way that only a relatively small height is provided in the stroke direction, the moving mass is significantly reduced. Such an almost disk-shaped form of the evasive piston would, however, in the event of rapid movements result in an increased tendency to incline in the guideway of the evasive piston in the interior of the associated storage space, and it is therefore proposed according to the invention to provide a corresponding guide, via which at the same time appropriate throttling of the stroke of the evasive piston, the desired injection law can be adhered to precisely, even with rapid and small strokes.

Due to the low overall height of the evasive piston, its inertial mass and thus its opening time is reduced. As a result, the dynamic opening pressure of the evasive piston and the valve needle can be selected to be higher, as a result of which the pre-injection quantity between opening the valve needle and opening of the evasive piston becomes less sensitive to scattering and greater, without the entire pre-injection thereby taking longer. This measure also has a desired effect at lower speeds than at higher speeds, since the dynamic opening pressure rises considerably above the speed. The increase in the statically set opening pressure, however, has an approximately constant effect over the speed. With the increasing dynamic opening pressure, there is an ever smaller increase in the injection quantity per unit of time. The damping acting on the evasive piston can thus be reduced, as a result of which the duration of the pre-injection is reduced, in particular at a higher speed, which leads to an injection break in degrees of crank angle that is approximately the same length in the predominant speed range of the pre-injection. Finally, the low design of the escape piston reduces not only its mass, but also the overall height of the entire pump nozzle, which is always welcome due to the installation conditions.

According to a preferred embodiment, the design is such that the diameter of the guide extension is smaller than the diameter of the sealing edge of the alternative piston facing the storage space, which results in a construction that is particularly simple in terms of production technology.

The stroke-dependent design of the cross section of the throttle opening is advantageously made such that the pin has its largest effective cross section at the point which interacts with the limiting plate at the beginning of its stroke, thereby ensuring that at the beginning of the stroke the Damping piston the greatest damping occurs, whereby the duration of the pre-injection is reduced, especially at high speed and the injection pause is adhered to exactly. A structurally simple design of this desired throttle characteristic or damping can be achieved in that the limiting plate has a narrow throttle lip or a throttle edge delimited by two side surfaces running at an acute angle to one another, the adaptation to the respectively desired laws being able to be improved in that the pin has a chamfer or recess which, over the length of the stroke of the evasive piston, delimits a cross-section with a different cross-section with the limiting plate. An asymmetrical design of the throttle cross section favors the desired damping characteristic, the design preferably being such that the recess has a triangular or trapezoidal cross section, and that the surfaces of the recess inclined to the longitudinal axis of the escape pistons have a different angle with the longitudinal axis lock in. Particularly favorable damping conditions could be achieved in that the cross-sectional area of the throttle opening corresponds to 1/25 to 1/500, in particular 1/50 to 1/200, of the circular bottom surface.

With regard to the stroke-dependent damping of the evacuation piston and the reduction of the moving masses, the quantity metering can above all be measured more precisely than with relatively slow and largely undamped displaceable evacuation pistons. A further improvement in the subdivision of pre-injection and main injection can be achieved in combination with such a more precise metering of the amount via a defined control of the stroke movement of the nozzle needle. The training is preferably made such that the nozzle needle, at its end facing away from the spray openings, is immersed in a second damping chamber which can be filled with fuel and has a pressure pin which is surrounded by a fixed shoulder which forms a stop for a shoulder of the nozzle needle, and that spatially fixed shoulder with the pressure pin during the lifting movement of the nozzle needle delimits a throttle opening which is connected to the damping space and which opens into a drain and / or another space. The throttling of the stroke of the nozzle needle takes place in the opposite direction to the throttling of the stroke of the evasive piston, as a result of which opening and closing occurs rapidly in the area of the pre-injection, since the stroke of the nozzle needle is limited by the throttling or damping of this first phase. An even clearer improvement consists in first of all realizing a rapid opening stroke of progressive damping in the area of the pre-injection, whereby the opening movement of the nozzle needle is increased and at the same time the path covered by the nozzle needle during the opening stroke can be restricted, whereby the closing movement can be initiated more quickly. Such training can be achieved in that the cross section of the throttle opening between The pressure pin and the fixed wall of the damping chamber can be varied as a function of the stroke of the nozzle needle. The stroke movement of the nozzle needle is delayed and reduced by the throttle opening between the nozzle spring chamber wall and the pressure pin. With the smaller stroke, on the one hand, the duration of the closing of the nozzle needle is shorter and, on the other hand, less fuel is returned to the high-pressure chamber due to the displacement effect of the closing needle, which leads to a greater pressure drop in the pre-injection between opening the evasive piston and closing the valve needle after reaching the closing pressure leads. The reduction in the injection quantity achieved during the course of the injection has a desired effect at higher engine speeds than at low engine speeds. This in turn allows an increase in the statically set opening pressure, which causes an increase in the amount injected between opening the valve needle and opening the evasive piston.

The invention is explained in more detail below with reference to embodiments of the fuel injection nozzle according to the invention which are shown schematically in the drawing. 1 shows a longitudinal section through the middle part of a fuel injection nozzle according to the invention; 2 shows detail A of FIG. 1 enlarged and rotated by 90 °; 3 shows a plan view of FIG. 2; 4 shows detail B of FIG. 1 enlarged; 5 shows a variant of detail B, and FIG. 6 injection rate curves at low and at high speed for a fuel injection nozzle according to the invention.

In the arrangement according to Fig. 1, 1 represents the pump piston liner,

2 the nozzle body (partially torn open) with the nozzle needle

3 and 4 illustrate the nozzle needle spring which is arranged in a spring housing 5. 6 is the escape piston and 29 the calibration piston bush. The avoiding piston 6 consists of a cylindrical guide part 7, a sealing cone 8 and an extension 10 with grooves 11 and an end face 12 which faces the pressure chamber 14, on which the pump piston 13 also acts. The evasive piston 6 has a relatively low weight due to the small height of the cylindrical guide part 7 relative to the diameter, which can be driven even further by selecting a light material. Its inertia is therefore low. The extension 10 can serve as a hydraulic damping member and is provided as an additional guide. It acts as an attenuator in that when the pressure in the pressure chamber 14 rises, the fuel passes through the grooves 11 into the storage chamber 34 and acts on the control edge 9. As soon as the evasive piston 6 starts to move downward, fuel must flow through the grooves 11, which then act as throttles. Since the throttling effect depends on the effective length of the grooves 11, this decreases as the evasive piston 6 drops.

In addition to the damping by the grooved extension 10 of the evasive piston, the movement of the evasive piston 6 is also damped by the interaction of a pin 17 with the limiting plate or throttle plate 19.

The bottom surface 15 of the evasive piston 6 facing away from the storage space acts in a damping space 16 which is delimited by the evasive piston sleeve 29 and the throttle plate 19 and is penetrated by the pin 17 with a chamfer 18 which is part of the evasive piston 6. The chamfer 18 and the bore of the throttle plate 19 form a throttle point which dampens the downward movement of the evasive piston 6. The special design of the chamfer 18 will be discussed later.

In the spring housing 5, the nozzle needle spring 4 establishes a force connection between the upper and lower spring plates 20, 21. The lower spring plate 21 - is based on the Nozzle needle 3 from. Of this, only the upper part is shown, which consists of a stop shoulder 22 to which a pressure pin 23 is connected at the top. This pressure pin 23 penetrates an intermediate plate 24, which has a fixed shoulder 26 below and a throttle lip 25 above. The fixed paragraph 26 interacts with the stop shoulder 22. The throttle lip 25 delimits a throttle cross section with a chamfer 27 of the pressure pin 23. During the upward movement of the nozzle needle 3, the fuel is pressed out of the space 28 between the throttle lip 25 and the chamfer 27, whereby damping of the stroke movement of the nozzle needle can be achieved.

In the embodiment of FIG. 1, the position of the chamfer 27 is selected such that the damping effect in the position shown is the smallest at the beginning of the nozzle needle movement and then increases, in order to give a short stroke of the nozzle needle 3, particularly during the pre-injection. Two variants for the formation of this throttle point are described below.

In FIGS. 2 and 3, the evasive piston 6 is shown enlarged. It can be seen that the guide extension 10 is formed with a smaller diameter than that of the control edge 9 and gives freedom in the choice of the diameter of the extension 10.

The pin 17 with the chamfer 18 protrudes from the bottom surface 15 of the evasive piston 6 into the throttle plate 19 (in an uninterrupted line when the evasive piston 6 is in its uppermost position). The chamfer is selected here so that the damping effect is greatest in this position. If the evasive piston lowers, as is indicated by the dashed position 19 'of the throttle plate, the damping effect is reduced. 4 shows a variant of the nozzle needle stroke damping. The stepped throttle lip 25 'is formed with a cylindrical inner edge, the chamfer 27 of the pressure pin 23 is asymmetrical, and the transition 30 forms a sharp edge, while the transition 31 is continuous. As a result, the throttling effect is dependent on the direction of movement and on the actual stroke of the nozzle needle. Damping is not desirable when the nozzle needle is closed. Because of the risk of cavitation in space 28, it can even be harmful.

In the variant of FIG. 5, the same effect is obtained with a modified version. The chamfer 27 of the pressure pin 23 is essentially trapezoidal with end regions which are inclined at different angles and is delimited on one side by the plane 33 and on the other by the conical surface 32.

The throttle cross sections shown in FIGS. 4 and 5 can be designed analogously for the damping of the avoiding piston 6. Instead of the trapezoidal chamfer 27, for example, an essentially triangular configuration can also be used. The cross-sectional areas of the throttling points are a maximum of 1/25 and at least 1/500 of the bottom surface 15 or the surface of the shoulder 22.

When designing the throttle points for damping the movement of the evasive piston 6 and the nozzle needle 3, in particular details A and B, there is great freedom within the scope of the invention to adjust the throttle behavior by means of measures which are common in the art and to be adjusted in the desired manner by the stroke or depending on the direction of movement. It is of course also possible to profile the pressure pin 23 and the pin 17 of the evasive piston in a rotationally symmetrical manner without the chamfer 27. In the following, a pump nozzle according to the prior art (dashed lines) and a pump nozzle according to the invention are compared with the diagrams of FIG. 6 about the injection quantity curves at idling and at higher engine speeds. The injection process is divided into several phases:

Phase 1: Start of the pump stroke until the dynamic one is reached

Opening pressure of the nozzle needle, no delivery, phase 2: end of phase 1 until the dynamic opening pressure of the evasive piston is reached,

Phase 3: end of phase 2 until the nozzle needle closes, phase 4: injection pause until the dynamic opening pressure of the nozzle needle is reached again, phase 5: the main injection that follows.

At low engine speed, the main difference between the prior art and the subject of the invention is in phase 3. It can be seen that with a similar form of the pressure profile, the quantity drop occurs earlier and steeper, which would reduce the pre-injection quantity slightly. The now possible higher dynamic opening pressure of the lighter alternative piston increases the quantity to the original level and also reduces the cyclical scattering of the pre-injection process.

At high speed, the difference is also in phase 3. Because of the steeper pressure reduction, the drop in the injection quantity is steeper, which results in a considerable reduction in the pre-injection quantity. The combination with the lower mass of the alternate piston and the resulting higher dynamic opening pressure leads to a short, supported by a decreasing alternate piston damping (which was only necessary in the state of the art to ensure a sufficient pre-injection quantity at low speed) Pre-injection and one subsequent, pronounced injection pause. This effect is further enhanced by the damping which can be varied via the stroke.

The measures according to the invention thus lead to the desired injection profile in the particularly difficult dynamic conditions of a pump nozzle for high-pressure injection and high speeds.

Given the tolerances that can be achieved for the production of precision parts of fuel injection nozzles and the leakage rates that are acceptable for sealing to the low-pressure side, the height of the evasive piston 6 can be reduced to 10% of the diameter with suitable guidance by the guide extension 10. Depending on the selected production quality, a reduction in the overall height of the escape piston 6 by up to 90% of the diameter is possible. As a result, the mass of the escape piston 6 can be reduced by up to 70%, which results in an increase in the maximum storage rate due to a higher acceleration of the escape piston 6 with the same pressure difference between the damping chamber 16 and the pump chamber 14.

Since the pin 17 has a variable cross-section, it is possible to further change the speed of the evasive piston 6 given the course of the pressure difference which is effective between the pump cylinder 13 and the pressure difference which is effective downstream of the throttle point formed by the chamfer 18. Characterized in that the pin 17 has its largest effective cross-section at the point, which cooperates with the limiting plate 19 at the beginning of its stroke, an ever faster opening movement of the evasive piston and associated rapid termination of the pre-injection is made possible. As the movement of the evasive piston 6 progresses, the remaining throttling effect results in a corresponding damping of the movement, so that despite the low weight vibrations of the backup piston can be avoided with certainty. Overall, this results in a faster dynamic response behavior of the evasive piston, which is made possible in particular by the reduction in weight, wherein additionally the friction-like design of the evasive piston reduces the frictional forces counter to the stroke direction.

As already mentioned above, the additional damping of the lifting movement of the nozzle needle is used to support the improved response behavior of the alternative piston that can already be achieved by the design of the alternative piston, in order to divide the injection into a pre-injection and a main injection.

Claims

Claims:

1. Fuel injection nozzle, in particular pump nozzle, with a nozzle needle (3) which is spring-loaded in the closing direction, in which the pressure chamber in front of the seat of the nozzle needle communicates with a storage space (34) delimited by a spring-loaded evasive piston (6), the evasive piston ( 6) at its end facing away from the storage space (34), the pressure in a damping space (16) which can be filled with fuel is acted upon and has a pin (17) which extends into a plate (19) delimiting the damping space (16) and having an opening ) immersed, characterized in that the cylindrical guide part (7) of the evasive piston (6) has a purchasing knife to height ratio of 1: 0.1 to 0.4, that the evasive piston (6) on its side facing away from the storage space (34) has a pin (17) with a variable cross-section, which dips into the limiting plate (19), and that the evasive piston (6) has an F on its side facing the storage space (34) has guide extension (10) with grooves (11).

2. Fuel injection nozzle according to claim 1, characterized gekenn¬ characterized in that the diameter of the guide extension (10) is smaller than the diameter of the sealing space (34) facing sealing edge (9) of the evasive piston (6).

3. Fuel injection nozzle according to claim 1 or 2, characterized in that the pin (17) has its largest effective cross-section at the point which cooperates with the limiting plate (19) at the beginning of its stroke.

4. Fuel injection nozzle according to claim 1, 2 or 3 to 4, characterized in that the limiting plate (19) has a narrow throttle lip or a throttle edge delimited by two acute-angled side surfaces.

5. Fuel injection nozzle according to one of claims 1 to 4, characterized in that the pin (17) has a chamfer or recess (18) which over the length of the stroke of the evasive piston (16) has a throttle opening of different cross-section with the limiting plate ( 19) limited.

6. Fuel injection nozzle according to claim 5, characterized gekenn¬ characterized in that the recess (18) has a triangular or trapezoidal cross-section, and that the inclined to the longitudinal axis of the evasive piston (6) surfaces of the recess with the longitudinal axis form a different angle.

7. Fuel injection nozzle according to one of claims 1 to 6, characterized in that the cross-sectional area of the

Throttle opening 1/25 to 1/500, in particular 1/50 to 1/200, corresponds to the circular bottom surface (15).

8. Fuel injection nozzle according to one of claims 1 to 7, characterized in that the nozzle needle (3) on its the

End facing away from the spray openings into a second damping chamber (28) which can be filled with fuel and has a pressure pin (23) which is surrounded by a fixed shoulder (26) forming a stop for a shoulder (22) of the nozzle needle, and that the fixed shoulder (26) with the pressure pin (23) during the lifting movement of the nozzle needle (3) delimits a throttle opening which is connected to the damping space and which opens into an outlet (11) and / or another space (12).

9. Fuel injection nozzle according to claim 8, characterized gekenn¬ characterized in that the cross section of the throttle opening between the pressure pin (23) and the fixed wall of the damping chamber (28) is variable depending on the stroke of the nozzle needle (3).