WO1987006308A1

WO1987006308A1 - Injection valve for internal combustion engines

Info

Publication number: WO1987006308A1
Application number: PCT/AT1987/000024
Authority: WO
Inventors: Gottfried Haider
Original assignee: Voest-Alpine Automotive Gesellschaft M.B.H.
Priority date: 1986-04-15
Filing date: 1987-04-08
Publication date: 1987-10-22
Also published as: EP0262197B1; ATE53436T1; EP0262197A1

Abstract

Injection valve for internal combustion engines, provided with a nozzle body (10) with injection holes (11, 12) for the fuel and two coaxial spring-loaded valve needles co-operating with separate injection holes. The external hollow needle (7) has radial bores (14) and the inner valve needle is designed as a control piston (13) of which the jacket, in the region of the openings of the radial bores (14) of the hollow needle (7), has control edges formed of an annular recess (15). Leading from the recess in the jacket of the control piston (13) are ducts, or preferably an axial bore (19), which extend to a seating (20), arranged on the control piston (13), of a valve-closing element (21) which co-operates with the control piston, such as for example a tapered element or ball. After a pre-determined travel of the control piston (13) the recess (15) forming the control edges causes a pressure drop and closure of the relevant injection holes (12), as a result of which a separation is achieved between the pre-injection and the main injection initiated by the raising of the hollow needle (7).

Description

Injection nozzle for internal combustion engines

The invention relates to an injection nozzle for internal combustion engines with a nozzle body with spray holes for fuel and two coaxial valve needles, in which the outer hollow needle and. the inner valve needle is resiliently supported and cooperate with separate spray holes and the hollow needle has radial bores.

In order to divide the injection into a pre-injection and a main injection, in order to achieve more favorable emission behavior and at the same time to reduce noise and to achieve a higher efficiency, a design has become known, for example from DE-OS 31 13 475, in which one has two needles Nozzle is provided. An outer hollow needle contains a coaxially guided nozzle needle, both needles being spring-loaded and axially displaceable. The hollow needle has radial bores for connection to the pressure chamber of the inner valve needle. The needles interact with separate spray holes and the timing for the pre-injection and the main injection can be specified by suitable dimensioning of the springs and the pressure shoulders effective for lifting the needles from their seat. In such designs, the pre-injection and the main injection merge directly into one another, so that there is no sharp separation between the pre-injection and the main injection. In addition, coaxial tapered seats are required, which means that relatively complex machining is necessary to avoid tolerance problems. The start, the end and the duration of the pre-injection depend on wear and are not exactly defined. Because the inner needle is seated in the outer nozzle needle, the movements of the two needles are coupled to one another and a large volume is required between the valve and the spray holes. which entails the risk of the nozzle dripping.

From DE-OS 27 11 391 a fuel injection nozzle has become known in which a valve needle is guided coaxially in a hollow needle. Both needles are spring-loaded and interact with separate spray holes. The fuel is supplied via radial bores in the hollow needle inside to the nozzle tip, the sequence of the opening and the opening times of the spray holes assigned to the nozzle needles being able to be controlled depending on the spring forces and the surfaces of the nozzle needle that are acted upon. With this known design, the pre-injection and main injection thus merge directly into one another, so that a sharp separation of the injection processes is not possible.

Another known design according to DE-OS 27 10 216 has a control piston guided in a nozzle needle. The control piston releases additional spray holes after lifting the nozzle needle over a predetermined stroke via radial control edges. Since the pre-injection and the main injection are only controlled by a common control element, namely the nozzle needle, which contains the control piston, the advantages of pre-injection are lost at full load and at higher speeds. A clear distinction between pre-injection and main injection is also not possible with this training.

The invention now aims to provide an education of an injection nozzle of the type mentioned, which gives the opportunity to the preliminary and main ^'injection to separate clearly and to set the timing accurately and independently of the timing of the main injection. In addition, the invention aims to implement such a design with the least possible manufacturing effort. To solve this task, the inventor fertilizer essentially in that the inner valve needle is designed as a control piston, the jacket of which has control edges formed by an annular recess in the region of the mouths of the radial bores of the hollow needle, and that, starting from the annular recess of the jacket of the control piston, channels to one arranged on the control piston Seat of a valve closing member interacting with the control piston, such as a ball, or lead to a valve closing member connected to the control piston. The fact that a control piston guided in a substantially sealing manner in a hollow needle is provided, which cooperates with radial bores of the hollow needle, can initially be displaced independently of a movement of the hollow needle and only defined by the spring load of the control piston of the control piston to release spray holes. The fact that the control piston itself has seating surfaces for a valve closing element which interacts with the control piston means that the opening pressure ratios and the times can be precisely defined and the possibility is created in a simple manner of a self-centering closing element without complex double fitting, for example a ball to use as a valve closing element. When the control piston is designed with this valve closing element, the channels of the control piston must open outside the outlet cross-sections to be sealed by the closing element, which results in a somewhat higher production outlay. After a predetermined stroke of the control piston, the pressure is again reduced by the control edges of the control piston and the associated spray holes are closed in a defined manner before the main injection is initiated by lifting the hollow needle from its seat. At the same time as this main injection, the injection holes of the pre-injection are again released so that the full outlet cross section is available for the main injection. This in turn makes it possible to find sufficiency with lower injection pressures. The one that acts on the control piston Spring ^* can be supported in a simple manner against the hollow needle itself and can be of relatively small dimensions, so that the control piston can be moved with little inertia.

According to a preferred embodiment of the injection nozzle according to the invention, the channels of the control piston are formed by an axial bore connected to the annular recess, which is flared at the end face facing the spray holes, and this end face interacts with a valve ball. This conical extension allows the ball to be supported with lateral play, since it is always centered in relation to the conical sealing surface of the control piston. This self-centering design allows inexpensive production with high precision and, due to the small seat diameter, a smaller pressure area, which in turn leads to a reduction in the size of the compression spring. Such a small compression spring for the control piston can be conveniently accommodated inside the hollow needle.

The valve ball itself can rest against the bottom of the nozzle body, leaving channels to the spray holes of the nozzle body. In this way, a particularly short path is achieved between the valve seat and the spray holes, as a result of which a clean separation between pre-injection and main injection can be achieved even at very high engine speeds, with no dripping occurring after the main injection. At the same time, a favorable flow pattern is achieved between the ball valve and the spray holes, whereby the fact that the valve seals against the control piston means that less acceleration is required for opening, which makes this design particularly suitable for high speeds.

Alternatively, the design can be such that the hollow needle has a blind hole in which the spray holes facing end wall, a bore for the connection to the spraying holes associated with the control piston is arranged in the nozzle body, that the hollow needle cooperates with a seat surface of the nozzle body on a larger radius than the spraying holes controlled by the control piston and that the valve ball and, if applicable, a channel-free ball support between the control piston and the end wall of the blind hole facing the spray holes are arranged. With such a configuration, the tip of the nozzle body is largely protected and tolerance compensation is achieved by the optionally provided ball support as a separate component. With such a design, an accurate manufacture of the blind hole bottom is not necessary.

According to a further preferred embodiment of the injection nozzle according to the invention, in its end region of the bore facing away from the needle tip, the hollow needle has a spring space for receiving the spring acting on the control piston. The measure of providing the spring chamber in the bore itself is due in particular to the fact that the control piston has only a small pressure area and the opening pressure for the pre-injection is low and can therefore be supported with relatively low spring forces.

To limit the stroke of the control piston, the spring chamber can advantageously be locked with a pressure pin that has an adjustable stop for the control piston. This adjustability of the stop allows the pre-injection quantity to be set exactly and simplifies processing and assembly.

According to a preferred embodiment, the design is such that the nozzle has separate feed lines for the main injection and the pre-injection, and that a control pressure which can be acted upon by a speed-dependent pressure, in particular the backing pump pressure, is introduced into the feed lines. Slider is switched on and that the control slide has a releasing or throttling cross-section in the feed lines depending on the pressurizing pressure. By switching on a control spool, which can be acted upon by a speed-dependent pressure, in particular by the pre-pump pressure, in the separate feed lines, it is possible to increase the time interval between the start of injection between the pre-injection and the main injection as the engine speed increases, thereby creating a clear separation between the pre-injection and the main injection over a further speed range is achievable. By changing the cross-section in the feed lines through the control valve, there is also the possibility of changing the quantitative ratio between the pre-injection and the main injection.

Since a very high pressure is built up in the feed lines before the start of injection, the control slide is preferably switched into the feed line for the pre-injection and into a bypass line for the line for the main injection, as a result of which the stress on the control slide can be significantly reduced since only a part of the high-pressure main injection quantity is directed through the spool. Preferably, the procedure is such that when the cross section in the feed line to the main injection is throttled, the control slide releases an enlarged cross section in the feed line to the pre-injection, as a result of which the quantitative ratio between the pre-injection and the main injection is shifted in favor of the pre-injection as the speed increases.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. In this Fig.l show schematically a pump-nozzle assembly, wherein the details of the nozzle can not be found in this figure. 2 shows an enlarged illustration of a first embodiment of the injection Nozzle shown in longitudinal section. 3 shows a section along the line III-III of FIG. 2 and FIG. 4 shows an enlarged illustration of the lower end region of the nozzle according to FIG. 5 shows a modified embodiment of a nozzle according to FIGS. 2, 3 and 4, in which the ball of the valve is mounted on a ball support. Figure 6 shows a section along the line VI-VI of Figure 5. Fig. 7 shows the injection pressure curve over the camshaft angle for different speeds. Fig. 8 shows in a modified embodiment a section through a control spool switched into the supply lines and Fig. 9 shows a section along the line IX-IX of Fig. 8. Finally, in Fig. 10 the injection pressure curve over the camshaft angle for different speeds is at Use of a control slide shown in FIGS. 8 and 9.

In Fig.l a pump-nozzle assembly is shown, in which the pump piston is designated 1. Following the working chamber 2 of this pump piston, a check valve 3 is provided, from which fuel reaches the nozzle 6 via supply lines 4 and 5 for the main injection and the pre-injection. The nozzle contains nozzle needles 7, the nozzle needle spring for the outer valve needle being denoted by '8. The nozzle needle spring 8 is designed as a helical spring and is supported on a spring plate 9 which cooperates with the outer nozzle needle via a spherical bearing.

The nozzle body is designated by 10 and contains spray holes 11 and 12, the details of the configuration of the nozzle 6 being shown, for example, in FIG.

In FIG. 2 it can be seen that within the outer nozzle needle 7 a control piston 13 is sealingly guided in the radial direction and displaceable in the axial direction. The outer nozzle needle 7, which is designed as a hollow needle, has radial openings 14, which open into an annular groove 15 of the control piston 13 in the rest position shown. The control piston 13 is resiliently supported by a helical spring 29 contained in the interior of the hollow nozzle needle 7. To secure the spring in the hollow needle and to adjust the spring force, a pressure pin 16 is provided as a closure piece for the bore of the hollow nozzle needle 7, which has a pin-shaped extension 17 as a stop for a pin-shaped extension 18 of the control piston 13. The free distance between these two stops 17 and 18 determines the possible pre-injection quantity.

When the supply line 5 is pressurized with fuel under pressure, pressure builds up via the radial openings 14 and the annular groove 15 in the interior of the control piston 13, an axial bore 19 being provided via which this pressure acts on a valve seat 20. When the force of the spring 29 loading the control piston is exceeded, the control piston 13 lifts with its valve seat 20 from a valve closing member formed by a ball 21, as a result of which the fuel is sprayed out via the spray holes 12 located on a smaller radius. When the control piston 13 is lifted, the lower edge of the ring-shaped recess 15 grinds over the radial openings 14 of the outer hollow needle 7, so that the further supply of fuel under pressure is prevented. Under the force of the spring 29, the control piston 13 with its valve seat 20 can in turn come into sealing contact with the ball 21, the intermediate hollow needle 7 being lifted from its seat in the meantime by the main injection pressure built up via the feed line 4 and the shoulders 22, and the releases larger 11 spray holes. At the same time, however, the spray holes 12, which are on a smaller radius, are released again. Details of this design according to Figure 2 can be seen in Figures 3 and 4. 3 shows the annular recess 15, which is connected via the radial bores 14 in the hollow needle 7 to the inlet bore 5 for the pre-injection fuel quantity.

From the illustration according to FIG. 4 it can be seen that after the valve body 13 has been lifted off from the closing member, which is formed by the ball 21, the fuel quantity supplied via the axial bore 19 of the control piston 13 can pass the valve ball 21 into the spray holes 12 . With this release of the spray holes 12, the seat surface 20 of the control piston 13 lifts off the ball 21 independently of a displacement of the outer hollow needle 7. After the seat 20 has been lowered again onto the ball 21 and the force required for lifting the hollow needle 7 has been exceeded, the hollow needle 7 lifts off its seat 22 at the base of the nozzle body 10, so that the spray holes 11 and the spray holes 12 are available for the main injection.

5 and 6, the hollow needle 7 has a blind hole 23, the end wall 24 facing the spray holes 11 and 12 of which has an axial bore 25 for supplying fuel to the spray holes 12. On the end wall 24, a support part 26 is fixed, which carries the ball 21 representing the valve closing member and allows the free passage of fuel to the axial bore 25. For this purpose, as can be seen from FIG. 6, the support part 26 has webs 27, between which openings 28 remain free.

The seat surface 20 of the control piston 13 is conical, as can be seen in particular in FIG. 5, so that a loose support of the ball 21 as a valve closing member on the base or the end wall 24 of the blind hole 23 is sufficient, to ensure a securely sealing closure between valve ball 21 and seat surface 20.

In such a configuration with a control piston, pressures between 100 and 150 bar are sufficient as the pre-injection pressure, the main injection being able to be achieved from pressures of over 200 bar, for example 240 bar. As soon as the injection pressure has dropped below the closing pressure, all the spray openings are closed at the same time.

The injection pressure curve over the camshaft angle can be seen from FIG. 7. At the speeds of 400, 1300 and 2200 revolutions per minute shown in comparison, the injection pressure between the pilot and main injection drops to zero for all embodiments, so that a clear separation of the pilot injection and the main injection is achieved at any speed.

FIG. 8 shows a modified embodiment, a control slide 29 being arranged in a slide seat 30 after the check valve in the inlet lines. 5 again designates the feed line for the pre-injection, while the feed line 4 for the main injection is indicated by dashed lines. The control slide 29 is switched into the feed line 5 and into a bypass line 31 of the feed line 4 for the main injection. The control slide has annular recesses 32 in the area of the lines 5 and 31 on its circumference. By applying a speed-dependent pressure, in particular the fore-pump pressure, the control slide 29 is displaced in the direction of arrow 33 against the force of a compression spring 34 arranged inside the control slide, whereby the cross section exposed in the feed line 5 by the recess 32 is increased , while the cross section released in the bypass line 31 is reduced. It therefore results with increasing speed and therefore increasing Control pressure a shift in the quantity ratio in favor of the pilot injection. With 35 O-rings for the seal are indicated.

9, the annular recesses 32 on the circumference of the control slide 29 can be clearly seen and the inlet lines are indicated by dashed lines. It is again clear that by moving the control slide 29 different cross sections in the lines 5 and 31 are released.

If a control slide valve according to an embodiment according to FIGS. 8 and 9 is used, an injection pressure curve results, as shown in FIG. 10. In addition to a separation between the pre-injection and the main injection, there is also a shift in the quantity ratio in favor of the pre-injection for increasing engine speeds in comparison with FIG Curve results.

Claims

Claims:

1. Injection nozzle for internal combustion engines with a Düsen¬ body with spray holes for fuel and two coaxial valve needles, in which the outer hollow needle (7) and the inner valve needle (13) are resiliently supported and cooperate with separate spray holes (11,12) and the Hollow needle has radial bores, characterized in that the inner valve needle is designed as a control piston (13), the jacket of which has control edges formed by an annular recess (15) in the region of the openings of the radial bores (14) of the hollow needle (7), and that, starting from the annular recess (15) of the casing of the control piston (13), channels to a seat (20), which is arranged on the control piston, of a valve closing element (21) which interacts with the control piston, such as, for example a ball, or lead to a valve closing member connected to the control piston (13).

2. Injection nozzle according to claim 1, characterized in that a spring (29) acting on the control piston (13) is supported against the hollow needle (7).

3. Injection nozzle according to claim 1 or 2, characterized in that the channels of the control piston (13) of an axial to the annular recess (15) connected

Bore (19) are formed, which on the spray holes

(12) facing end face is flared, and that this end face cooperates with a valve ball (21).

4. Injection nozzle according to claim 3, characterized in that the valve ball (21) bears against the spray holes of the nozzle body (10) at the bottom of the nozzle body while leaving channels.

5. Injection nozzle according to claim 3, characterized in that the hollow needle (7) has a blind hole (23), in the spray holes (11,12) facing the end wall (24) has a bore (25) for connection to the control piston ( 13) assigned spray holes (12) in the nozzle body (10) is arranged such that the hollow needle (7) cooperates with a seat surface of the nozzle body (10) on a larger radius than the spray holes (12) controlled by the control piston (13) and that the valve ball (21) and optionally a channel-free ball support (26) are arranged between the control piston (13) and the end wall (24) of the blind hole (23) facing the spray holes (11, 12).

6. Injection nozzle according to claim 1 to 5, characterized in that the hollow needle (7) in its end region facing away from the needle tip of the bore has a spring space for receiving the control piston (13) acting spring (29).

7. Injection nozzle according to claim 6, characterized in that the spring chamber with an adjustable stop (17) for the control piston (13) having a pressure pin (16) can be locked.

8. Injection nozzle according to claim 1 to 7, characterized gekenn¬ characterized in that the nozzle has separate inlet lines (4,5) for the main injection and the pre-injection that in the inlet lines (4,5) with a speed-dependent pressure, in particular with the Backing pump pressure, actable control slide (29) is switched on and that the control slide has a releasing or throttling cross section in the inlet lines depending on the pressurizing pressure.

9. Injection nozzle according to claim 8, characterized in that the control slide (29) in the feed line (5) for Pre-injection and in a bypass line (31) to line (4) for the main injection is switched on.

10. Injection nozzle according to claim 8 or 9, characterized in that the control slide (29) releases a larger cross-section in the supply line (5) for pre-injection when the cross section in the supply line (4) is throttled.