GB2353565A

GB2353565A - Fuel-injection valve

Info

Publication number: GB2353565A
Application number: GB0020026A
Authority: GB
Inventors: Patrick Mattes; Friedrich Boecking
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-08-25
Filing date: 2000-08-16
Publication date: 2001-02-28
Anticipated expiration: 2020-08-16
Also published as: GB0020026D0; FR2797915A1; JP2001082280A; GB2353565B; DE19940294A1

Abstract

The fuel-injection valve has a valve body 10, a nozzle needle 12, which is attached in a displaceable manner in the valve body, an actuating part 18, against which the nozzle needle 12 is supported, and a pressure piece 22 which is connected to a control pressure space 24 and uses the actuating part to control the opening and closing of the nozzle needle. In order to render it possible to reduce the pre-injected fuel volume, without requiring a rapid-switching solenoid control valve 30 for the fuel-injection valve, a spring 20 is disposed between the pressure piece 22 and the nozzle needle 12. The spring 20 is selected to modify the rigidity of the assembly formed by the needle 12, the actuating part 18 and the pressure piece 22. The spring 20 may be a coil spring, a metal sleeve with recesses (fig.5), a disc spring assembly (fig.6) or a rubber spring (fig.7). In a modification, the spring 20 is located between the actuating part 18 and the nozzle needle 12 by being housed in a sleeve 40 attached to the front end of the actuating part 18. In this arrangement, the front end 46 of the sleeve 40 acts as a stop for the needle, to determine a stroke H.

Description

2353565

DESCRIPTION FUEL-INjECTION VALVE

The invention relates to a fuel-injection valve having a valve body, a nozzle needle which is attached in a displaceable manner in the valve body, an actuating part against which the nozzle needle is supported, and a pressure piece which is connected to a control pressure space and uses the actuating part to control the opening and closing of the nozzle needle.

This type of fuel-injectioh valve is disclosed in DE 197 27 896 AI. The nozzle needle is opened and closed by virtue of changes in the pressure in the control pressure space. For this purpose a solenoid valve is provided which can open and close an outlet orifice of the control pressure space. If the solenoid valve is closed, a force is exerted upon the pressure piece by the pressure prevailing in the control pressure space, which force holds the nozzle needle closed against an opening force which is exerted upon the nozzle needle by the fuel which surrounds same. If the solenoid valve is opened the pressure drops by reason of the pressure medium flowing away from the control pressure space, so that the force exerted upon the pressure piece is smaller than the opening force exerted upon the nozzle needle, whereby the nozzle needle rises from an associated valve seat. Fuel is then injected into a cylinder of an internal combustion engine.

In order to optimize the process of the combustion of the injected fuel in the cylinder, it is possible to perform a preliminary injection, wherein prior to the commencement of the actual injection process a small quantity of fuel is injected into the cylinder. This serves to precondition the combustion chamber which enhances the efficiency of the combustion process, shortens the ignition delay during the main- 2 injection process and reduces combustion pressure peaks. The quantities of fuel injected during the preliminary injection are so small that the intrinsic rigidity of the assembly formed from the nozzle needle, the actuating part and the pressure piece has a considerable influence upon the required short opening of the nozzle needle.

In accordance with the present invention there is provided a fuel injection valve having a valve body, a nozzle needle, which can be attached in a displaceable manner in the valve body, an actuating part, against which the nozzle needle is supported, a pressure piece which is connected to a control pressure space and uses the actuating part to control the opening and closing of the nozzle needle, and a spring element disposed between the pressure piece and the nozzle needle.

Such a fuel-injection valve has the advantage that by selecting the spring constant of the spring element the intrinsic rigidity of the assembly consisting of the nozzle needle, actuating part and pressure piece can be adjusted in virtually any manner. In particular, where the solenoid valve remains unchanged it is possible to achieve an extremely small volume during the preliminary injection, without having to provide a particularly rapid solenoid valve for this purpose. In the case of a valve in accordance with the invention, a reduction in the pressure in the control pressure space does not actually directly cause the nozzle needle to be raised from the valve seat, but rather initially causes the length of the spring element to increase in the direction of the control pressure space. Only after the length of the spring element has increased by a certain amount does the nozzle needle rise from the valve seat. The opening pressure which then acts upon the nozzle needle ensures that the spring element is then compressed. As soon as the solenoid valve closes the control pressure space and therefore the pressure therein increases, the nozzle needle is 3 then closed without delay. It is thus possible to achieve a small quantity during the preliminary injection, without requiring a solenoid valve which switches in a particularly rapid manner. Furthermore, a particularly compact design of the fuel-injection valve is achieved, since with a suitable design of the spring elements only a small amount of installation space is required, in order to be able to adjust as required the intrinsic rigidity of the assembly consisting of the nozzle needle, actuating part and pressure piece.

The invention will be described hereinafter, by way of example only with reference to various embodiments which are illustrated in the attached drawings, in which Figure 1 is a schematic cross-section of a fuel-injection valve in accordance with the invention according to a first embodiment; Figures 2a to 2c show various characteristic curves of the fuel-injection valve in accordance with the invention; Figure 3 is a schematic sectional view of the region of the nozzle needle of a fuel-injection valve according to a second embodiment of the invention; Figure 4 is a schematic sectional view of the nozzle needle of the fuel injection valve of Figure 3; Figure 5 is a partial section view of a variation of a spring element which can be used in the fuel-injection valve in accordance with the invention; Figure 6 is a sectional view of a finther variation of a spring valve; and 4 Figure 7 is a schematic sectional view of a variation of a spring element which can be used in a fuel-injection valve in accordance with the invention.

Figure I illustrates a 2 port, 2 position-fuel-injection valve for a socalled "common rail"-inj ection system.. The injection system comprises a valve body 10, in which a nozzle needle 12 is disposed in a displaceable manner. The said nozzle needle cooperates with a valve seat 14, in order to control the injection of fuel, which is provided via a supply line 16, into a cylinder of an internal combustion engine [not illustrated].

Connected to the nozzle needle 12 is an actuating part 18 which is connected by means of a spring element 20 to a pressure piece 22. The pressure piece 22 protrudes into a control pressure space 24, to which leads a supply line 26 which is provided with a supply throttle. An outlet line 28, which is provided with an outlet throttle and can be opened and closed by a control valve 30 [illustrated here only schematically], leads off from the control pressure space 24. It is possible in particular to use a solenoid valve as the control valve.

The spring element 20 serves to adjust in the desired manner the rigidity of the assembly formed from the nozzle needle 12, the actuating part 18 and the pressure piece 22. It is possible to use the spiral spring illustrated in Figure I as the spring element. However, alternative embodiments are also possible, for example, the spring element shown in Figure 5 which consists of a metal sleeve 20 which is alternately provided with recesses 50 which extend starting from mutually opposite sides of the metal sleeve. Alternatively, it is also possible to use the spring element 20 shown in Figure 6 which consists of a disc spring assembly. It is also possible to use the rubber spring illustrated in Figure 7 which consists of a ring having a rubber spring element 79 vulcanized therein.

If the control valve 30 is closed, the fuel pressure effective in the control pressure space 24 produces a closing force which is greater than an opening force produced by the fuel in the region of the nozzle needle 12. The pressure piece 22 thus ensures that the nozzle needle 12 lies against the valve seat 14, so that no fuel is injected. At the same time, the spring element 20 is held in a pretensioned manner.

If the control valve 30 is opened, the pressure in the control pressure space 24 falls by reason of the fuel flowing away, so that initially the spring element 20 can be extended and is able to urge the pressure piece 22 into the control pressure space 24. The actuating part 18 is then also displaced in the direction towards the control pressure space 24, so that the nozzle needle 12 rises from the valve seat 14 and fuel can be injected. The stroke of the nozzle needle is defined by means of a stroke stop 32 which cooperates with a collar 34, formed on the actuating part 18, and thus determines a stroke H.

If the fuel valve is opened, a greater opening force acts upon the nozzle needle 12 than in the closed condition. This greater opening force can be attributed to the fact that in the open condition an additional surface of the nozzle needle 12 is influenced with the fuel pressure. By reason of the greater opening pressure, the spring element 20 is then compressed to a certain extent.

If the fuel-injection valve is to be returned to its closed position, the control valve 30 is initially closed, whereupon the pressure in the control pressure space 24 increases. The closing force which is exerted upon the pressure piece 22 is thus greater than the opening force which acts upon the nozzle needle 12, and by way of the spring element 20 and the actuating part 18, the closing part 22 returns the nozzle part 12 to a position in 6 which it lies against the valve seat 14. The spring element 20 is then further compressed to a slight extent.

The change in the opening and closing behaviour of the fuel-injection valve as achieved by reason of the spring element 20 will now be explained with reference to Figures 2a to 2c. In Figure 2b, the opening stroke of the control valve 30 is plotted over time. A first phase I is evident, in which the control valve 30 opens for a short period of time in order to achieve a preliminary injection. It can be seen that a second phase 11 follows on from this, wherein the control valve 30 is open for a longer period of time in order to render it possible for the main- injection process to be performed.

In Figure 2a, the dotted line serves to illustrate the stroke of the pressure piece 22 in the control pressure space 24. This stroke is compared with the stroke of the nozzle needle 12 (continuous line). It can be seen during phase I that the pressure piece 22 performs a considerably greater stroke than the nozzle needle 12, since after the control valve has been opened the spring element 20 is initially extended, which is demonstrated in the stroke of the pressure piece 22, while the nozzle needle 12 still lies against the valve seat 14. Only after the spring element 20 has extended to a certain extent, does the nozzle needle 12 rise from the valve seat. However, if the pressure piece 22 is moved in the direction towards the valve seat 14, this movement will be immediately transmitted to the nozzle needle 12, since the spring element has been tensioned once again after the nozzle needle rises, and said nozzle needle then closes the fuel-injection valve.

During phase II, a similar picture develops initially. At first, the pressure piece 22 performs a stroke before the nozzle needle 12 performs a stroke. However, if the pressure piece 22 has already performed its complete stroke, the nozzle needle 12 opens further, 7 since the spring element 20 is further compressed by reason of the opening pressure which increases as the nozzle needle 12 opens. If towards the end of phase II the control valve 30 is then closed, the pressure piece 22 is initially displaced and then the nozzle needle 12 is also displaced with a slight delay.

Thus, in comparison with a conventional fuel-injection valve, wherein the pressure piece is rigidly coupled to the nozzle needle, a fuel-injection valve in accordance with the invention serves to provide a smaller quantity of pre-injected fuel whilst the control valve maintains the same switching behaviour. This can be seen in the difference between the surfaces below the curves for the stroke of the pressure piece and the stroke of the nozzle needle for phase 1. However, when viewed relatively the difference for phase II is considerably less than with respect to the preliminary injection. It is therefore possible to achieve a considerably reduced preliminary injection in comparison with a conventional fuelinjection valve during a virtually constant main-injection of fuel.

Figure 2c illustrates the stroke for a pressure piece (dotted line) and the stroke for a nozzle needle (continuous line) corresponding to the illustration in Figure 2a, wherein a spring element is disposed with a lower level of rigidity between the pressure piece and the nozzle needle. It can be seen that in this case an extremely small nozzle needle stroke is performed in the event of a comparatively large pressure piece stroke during the preliminary injection. For phase II of the main-injection process, the nozzle needle is opened completely despite the low level of rigidity in the spring element.

Conventional spring rates for the spring elements used are in the order of 2 to 4 N/Lm.

One alternative embodiment of the fuel-injection valve in accordance with the 8 invention is illustrated in Figures 3 and 4. In the case of this embodiment, the spring element 20 is no longer disposed between the pressure piece 22 and the actuating part 18, but rather is disposed between the actuating part 18 and the nozzle needle 12. The spring element 20 is formed in this case as a spiral spring which is disposed inside a sleeve 40. This sleeve 40 consists of a curved metal piece which during assembly is attached, for example by means of a weld seam 42, to the front end of the actuating part 18 which serves as the guide portion. The slit 44 which is produced as the sleeve 40 is bent does not have to be closed.

The sleeve 40 serves on the one hand as a guide for the spring element.20. On the other hand, the front end 46, facing the nozzle needle 12, of the sleeve functions as a stop for the nozzle needle 12, so that a stroke H is determined.

With respect to the mode of function, the embodiment illustrated in Figures 3 and 4 corresponds to that of Figure 1.

Claims

9 CLAIMS

1. A fuel-injection valve having a valve body, a nozzle needle, which can be attached in a displaceable manner in the valve body, an actuating part, against which the nozzle needle is supported, a pressure piece which is connected to a control pressure space and uses the actuating part to control the opening and closing of the nozzle needle, and a spring element disposed between the pressure piece and the nozzle needle.

2. A fuel-injection valve according to claim 1, wherein the spring element is disposed between the actuating part and the nozzle needle.

3. A fuel-injection valve according to claim 1, wherein the spring element is disposed between the pressure piece and the actuating part.

4. A fuel-injection valve according to any of the preceding claims, wherein a stop is provided which as seen from the nozzle needle is disposed in front of the spring element.

5. A fuel-injection valve according to claim 2 and claim 4, wherein attached to the actuating part is a sleeve whose end face facing the nozzle needle forms the stop, the spring element being disposed inside the sleeve.

6. A fuel-injection valve according to claim 3 and claim 4, wherein the stop cooperates with a collar on the actuating part.

7. A fuel-injection valve according to any of the preceding claims, wherein the spring element (20) is formed by means of a disc spring assembly.

8. A fuel-injection valve according to claim 7, wherein the spring element is formed by means of a rubber spring.

9. A fuel-injection valve according to claim 7, wherein the spring element is formed by means of a metal sleeve which is provided with recesses which start alternately from mutually opposite sides of the metal sleeve.

10. A fuel-injection valve according to claim 7, wherein the spring element is formed by means of a spiral spring.

11. A fuel-injection valve substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.