EP0090296B1 - Needle-valve injection nozzle - Google Patents

Abstract

A control device and method for opening and closing the nozzle of a fuel injector. The control device includes first and second cavities which are formed in the body of the fuel injector, with the second cavity being located close to the nozzle. First and second variable pressure supply chambers are connected to the nozzle and to the two cavities by several fluid passages. A spool valve and a needle valve are positioned in the first and second cavities, respectively, with the spool valve abutting a stem which projects into and terminating in the second cavity. Also situated in the second cavity between the stem and the needle valve is a spring which forms a link therebetween. The spool valve is pressure-actuated by a difference of pressure in the first and second pressure chambers to move between an open and a closed position. In the open position, fluid flow from one of the pressure chambers is permitted through the spool valve and to the second cavity. As the fluid pressure in the second cavity increases to a value greater than the compressive force of the spring, the needle valve will open and allow fluid flow through the nozzle of the fuel injector. As the spool valve moves to its closed position, it compresses the spring further and then urges the needle valve to close. The needle valve closes prior to a drop in fluid pressure in the second cavity.

Description

The invention relates to a fuel injector with a needle piston arranged in a first cylinder chamber, which is provided with a valve needle for opening and closing an injection opening and which from a valve closing position by the injection pressure under tension of a spring by an amount corresponding to the opening travel into an Valve opening position is displaceable, with a control piston which is arranged displaceably in a second cylinder chamber and which, when the needle piston is in the valve closed position, is in the end position remote from the needle piston, which is supported against the spring and which leads to a fuel channel leading to the first cylinder chamber in the area between the needle piston and the valve opening controls, with the fuel channel being connected to a fuel pressure source in the end position remote from the needle piston, and which, when the valve is in the open position to initiate the valve closing movement, the spring during its adjustment movement in the direction of the Na delkolben spans by a further amount and thereby separates the fuel channel from the fuel pressure source.

With the increasing demands for lower petrol consumption, less pollution, etc., the demands on internal combustion engines and their aggregates are becoming ever greater. Injectors have also undergone remarkable further development in recent years, and it has been recognized that better combustion, less smoke and lower exhaust gases can be achieved by quickly stopping the fuel injection process.

In the nozzle from which the invention is based (US-A-2 813 752), the needle piston opens twice per work cycle, first for a pilot injection and then for a main injection.

GB-A-529 141 also discloses an injector with which two injections are achieved in one cycle. For this purpose, two pistons lying next to each other are provided. A piston is acted upon at one end by the system pressure and at the other end by a spring, the system pressure being used to move the piston downwards and the spring to move the piston upwards. The upward movement of the piston and thus the closing of the outlets by the needle piston occurs very slowly.

DE-A-2 704 688 shows an injection nozzle for quick or abrupt termination of the fuel injection process. In particular, a needle piston is provided which has at its upper end a piston which is displaceable in a pressure chamber and which is loaded by a spring in the direction of the closed position. The pressure chamber is connected to a pressure storage device, which comes into effect when the pressure in the supply line drops. As a result, the piston is additionally acted upon, so that the needle piston is returned to its closed position under the action of the spring and the pressure from the pressure storage device.

FR-A-2 336 563 shows two pressure sources and pumps.

In contrast, the object to be achieved with the invention is seen in designing the fuel injector in such a way that the closing pressure is greater than the opening pressure while maintaining a rapid tearing off of the injection process.

This object has been achieved according to the invention in that the control piston is acted upon on the side remote from the needle piston by a second pressure source, a control pressure source and on the side near the needle piston by the first, the fuel pressure source, and in that the pressure of the fuel pressure source and the pressure of the control pressure source for introduction and implementation of the valve opening and closing movement are controllable, the second cylinder space being connectable to a collecting container in its section which can be acted upon by the control pressure for pressure relief.

In this way, the needle piston and the control piston will be in an unloaded state, ie if the engine has not yet been started, in their starting positions, in which the needle piston is in its valve-closed position and the control piston is in its opposite or distant end position from the needle piston . When the nozzle and thus the needle piston are acted upon, pressure builds up in the nozzle, which finally lifts the needle piston from its seat and displaces it against the action of the spring, which is thereby compressed. The displacement by the injection pressure lasts until the maximum injection pressure is reached - in this state, the needle piston will assume a kind of floating position - or until the needle piston leads against a stop. The control piston must now be actuated to close the needle piston. The time of the shift is made dependent on various parameters of the internal combustion engine, and the amount of fuel to be injected can be precisely determined depending on the selection of the closing time. When the control piston is moved out of its end position, however, the spring - this time from the opposite side - is compressed by a further amount. The opening pressure does not have to be reached immediately, but possibly with a time delay. However, if the resulting force from the pressure force and spring force overcomes the opening pressure or the opening pressure is suddenly reduced, the spring will move the needle piston back into its valve closing position. Then the control piston can be relieved and the spring pushes it back into its starting position. in the seen as a whole, the spring for closing the needle piston is additionally tensioned, so that ultimately there is a closing pressure which is above the opening pressure.

For easy closing of the fuel channel guiding the fuel to the needle piston, it is provided according to the invention that a channel is provided in the control piston, which connects the fuel channel with another channel leading to the fuel pressure source in its end position remote from the needle piston. By this measure, the channel designed according to the invention as an annular channel in the control piston is gradually interrupted when it is acted upon, so that the connection to the fuel channel guiding the fuel to the needle piston, so that the fuel flow is initially throttled and then completely prevented. During throttling, the injection pressure remains so high that the needle piston remains in its open position.

The fact that the valve opening position of the needle piston is limited by a retaining ring means that the injection pressure can be relatively high and the needle piston closes with a time delay when the control piston is acted on.

For the possible connection of the second cylinder chamber to the collecting container, it is proposed according to the invention that the second cylinder chamber is provided with a relief opening which is opened from the side of the control piston remote from the needle piston when or after the connection of the fuel channel to the fuel pressure source is interrupted.

• Fig. 1 eine Brennstoffeinspritzdüse, teilweise im Schnitt;
• Fig. 2 die Brennstoffeinspritzdüse nach Fig. 1, jedoch in einem größeren Maßstab, wobei der Steuerkolben sich in seiner obersten Stellung und der Nadelkolben in seiner geschlossenen Stellung befindet;
• Fig. 3 eine ähnliche Darstellung wie Fig. 2, jedoch den Steuerkolben in einer Zwischenstellung und den Nadelkolben in seiner teilweise geöffneten Stellung zeigend, und
• Fig. 4 die Brennstoffeinspritzdüse nach Fig. 1 mit einem sich in seiner untersten Stellung befindlichen Steuerkolben und einem sich in seiner geschlossenen Position befindlichen Nadelkolben.

In the drawing, an embodiment of the invention explained in more detail below is shown. It shows:

• Figure 1 is a fuel injector, partially in section.
• Figure 2 shows the fuel injector of Figure 1, but on a larger scale, with the control piston in its uppermost position and the needle piston in its closed position;
• Fig. 3 is a view similar to Fig. 2, but showing the control piston in an intermediate position and the needle piston in its partially open position, and
• Fig. 4 shows the fuel injector of Fig. 1 with a control piston in its lowermost position and a needle piston in its closed position.

In FIG. 1 of the drawing, a fuel injection nozzle is designated by 10, its nozzle body by 12, and a nozzle tip provided at one end of the nozzle body by 14. Via a thread 16, the nozzle body 12 can be screwed into a cylinder head of an internal combustion engine, which is not shown for the sake of simplicity, in such a way that its nozzle tip 14 is connected to a combustion chamber. Fuel is injected into this combustion chamber in a fine veil, for which purpose a few injection openings 18 are provided in the nozzle syringe 14. However, in order to be able to control the injection process precisely, a control pressure source 20 and a fuel pressure source 22 are first provided in the nozzle body 12 of the fuel injection nozzle 10, each of which is connected to a collecting container 24 and 28 and a separate pump 26 and 30. In this case, the control and fuel pressure sources 20, 22 can be designed as a liquid supply chamber with variable pressure and correspond to the control and metering chamber, as is already the case with some injection nozzles. With these injection nozzles, the control space serves to control the injection timing and the metering space to determine the injection quantity. A control device 32 is also inserted in the nozzle body 12, which regulates the fuel flow through the fuel injection nozzle 10. In detail, it has a first and a second cylinder space 36 and 34, which are axially aligned with one another in the nozzle body such that the first cylinder space 36 comes to lie in the immediate vicinity of the nozzle tip 14. The cylinder spaces thus lie between the pressure sources to which they are connected, as well as to one another, and the nozzle tip, their upper and lower ends being denoted by 38, 40 and 42, 44. However, as far as their connection to the pressure sources is concerned, the upper end 38 of the cylinder space 34 is connected to the control pressure source 20 via a first channel 46 and its lower end 40 as well as a point 50 which is approximately midway between the upper and lower ends 38 and 40 is connected to the fuel pressure source 22 via a second line 48. A fuel channel 52 connects the second cylinder space 34 approximately in the area of the point 50 to the lower end 44 or end area of the first cylinder space 36. A relief channel or a relief opening 54 in turn connects the second cylinder space 34 to a collecting container 56 in the area of its upper end 38 , which can be connected to the collecting container 24 and / or 28. Instead of the relief bore 54, a relief valve can also be provided in the first channel 46 and the collection containers could also be integrated in the injection nozzle.

The control device is also equipped with a first valve, a control piston 58, which is displaceable in the cylinder space 34 and bears against a rod 60. The latter extends into the first cylinder space 36 and is connected there to a transverse part 62, such as a pin. Furthermore, a channel 64 or an annular groove is machined into the control piston, so that two piston pieces are formed, between which a connection of the channel 48 to the fuel channel 52 is created, provided the control piston 58 is in its position in FIG. 1 or 2 shown top position. The control piston 58 is displaceable between its end positions, that is to say between its uppermost position shown in FIGS. 1 and 2 and its lowest position shown in FIG. 4 by pressure differences which are created in the pressure sources 20 and 22. These pressure differences act on the upper and lower ends 38 and 40 of the second cylinder chamber 34 and thus also on the control piston 58. However, the control piston 58 is adjusted downward from its position shown in FIG. 1 or 2, in the direction of its lowest position , then the channel 64 will no longer be aligned with the point 50, so that the fuel can no longer get from the channel 48 to the fuel channel 52 or vice versa. On the other hand, the control piston 58 in this position will prevent exhaust gases from the combustion chamber from entering the fuel pressure source through the channels 52 and 48.

A second valve, a needle piston 66 with step pressure surfaces, is provided in the first cylinder space 36 and can be moved between an open and a closed position. In this, fuel can escape through the nozzle tip 14 once or the leakage of fuel is prevented. The upper surface of the needle piston 66 is designated 68, an interface 70 and a conical base 72. The latter sits on a stiz 73 when the needle piston 66 is in its closed position. In this position, the area exposed to the fuel is smaller than the upper surface 68 because the fuel can only affect the intermediate surface 70. However, if the needle piston 66 is in its open or upper position, the fuel can act on the base surface 72 in addition to the intermediate surface 70. The needle piston 66 is displaced between its open and closed positions by the movement of the control piston 58 and the fuel pressure which, as stated, can act on the intermediate surface and additionally on the base surface. This double actuation enables the control device 32 to react to a drop in pressure on the channel 64 at a point in time at which a drop in pressure has not yet been determined in the first cylinder space 36. This has the effect that the needle piston 66 is already pressed into its closed position before it was able to determine a pressure drop in the first cylinder space 36.

In the first cylinder space 36 there is also a spring 74 between the upper surface 68 of the needle piston 66 and the transverse part 62, which serves to push the control piston 58 and the needle piston 66 away from one another. The upward movement of the needle piston is limited by a retaining ring 76, which is also arranged in the first cylinder space.

The mode of operation of the fuel injector 10 is explained below with reference to FIGS. 2 to 4. FIG. 2 shows the starting position in which there is no pressure difference in the pressure sources 20 and 22 and the pressure influences the movement of the control device 32. In this position, the control piston 58 is in its uppermost position and fuel can pass through the channel 64 from the channel 48 into the fuel channel 52 into the needle piston 66, which is then still in its closed position, in which the base surface 72 Seat 73 closes. In this position, the spring 74 is slightly compressed, whereby the control piston 58 and the needle piston 66 are pressed away from each other. The fuel pressure in the two pressure sources 20 and 22 is then increased via the pumps 26 and 30 to a predetermined value, which then acts on the intermediate surface 70 and balances the force of the spring. This equality of pressure allows the needle piston 66 to remain in its seat, but is such that the needle piston opens immediately with an additional pressure increase. If the pressure in the two pressure sources 20 and 22 is increased at the same time, it will propagate to the intermediate surface 70 of the needle piston 66 and move it upward against the force of the spring 74. The needle piston 66 is opened and fuel can enter the combustion chamber of the internal combustion engine through the injection openings 18 in the nozzle tip 14. During the upward movement, the area of the needle piston 66 that is exposed to the fuel pressure is also increased, since the fuel pressure then acts not only on the intermediate surface 70 but also on the base area 72. As a result, the pressure increase becomes so great that the spring 74 is no longer able to close the needle piston 66. He therefore remains in his open position.

At a predetermined point in time, a pressure difference is then generated in the pressure sources 20 and 22, the pressure in the fuel pressure source 22 being lower, so that the control piston 58 moves downward in the direction of its second position. This is illustrated in FIG. 3, from which it can be seen that the channel 64 is no longer aligned with the channels 48 and 52 or with the location 50. As a result, the fuel flow between the channels 48 and 52 is initially throttled and later completely prevented. At the same time, the spring 74 is further compressed during this downward movement, since the transverse part 62 then acts on the spring as a result of the rod 60 resting against the control piston. The spring 74 is compressed until its spring force corresponds to the difference in the pressures which act on the upper side of the control piston 58 and on the intermediate surface 70 and base surface 72 of the needle piston 66. At about such a time, particularly when the pressure continues to rise, the spring 74 acts as a mechanical rod and causes the needle piston 66 to move downward is directly dependent on the downward movement of the control piston. Immediately before the fuel connection via the channel 64 is completely interrupted due to the downward movement of the control piston 58, the force of the spring will correspond to the pressure difference that prevails between the pressure sources 20 and 22. The needle piston 66 will then begin its downward movement again. This can take place because after the channel 64 has been pushed out of the area of the location 50 and therefore no more fuel can flow through the channel 64, the pressure at the intermediate surface 70 and the base surface 72 begins to decrease. The pressure drop is based on two factors, namely that a part of the fuel will emerge through the nozzle tip and on the other hand the fuel flow from the fuel pressure source 22 is throttled or completely prevented. The pressure in the fuel source will drop until the needle piston 66 is again in its closed position, in which no more fuel can escape through the nozzle tip. Since in this process the pressure force of the spring 74 is higher than during the upward movement of the needle piston 66 and the pressure below the needle piston 66 constantly decreases, the needle piston 66 will close very quickly. It can be seen from this that the force required to close the needle piston 66 is greater than the force required to open the needle piston. This feature ensures that the fuel flow through the nozzle tip in the combustion chamber of the internal combustion engine is cut off sharply. The greater force also prevents the needle piston from reopening prematurely, so that an unintentional, two-time injection is prevented. In Figure 4, the control piston 58 is located in its lowest position, and the needle piston assumes its closed position or is in its closed position. In this position, all fuel fed through the channel 46 from the control pressure source 20 will flow out through the relief opening 54. The latter serves to prevent damage to the control device 32, which could result from the fact that the control piston 58 could impact against the lower end of the second cylinder space. Although the pressure difference between the pressure sources is large, the valve piston 58 will not strike the lower end 40, as an increasingly larger area of the drilling opening of the relief opening 54 in the upper end 38 of the cylinder space is released during the downward movement. It should also be noted here that the channel 64 has already been moved out of the area of the location 50 before the upper surface of the control piston 58 has been moved below the drilling opening of the relief opening 54. This ensures that the fuel flow on channel 64 has already been throttled or stopped before pressure can be released via the relief opening. The time delay also ensures that the needle piston 66 remains in its closed position and thus prevents a second unwanted injection process from taking place.

At a further predetermined point in time, the pressure difference between the pressure sources is reduced or built up again to zero, as a result of which the control piston 58 is moved upwards by the force of the spring 74. The spring 74 relaxes over its initial length, as indicated in FIG. 2, and a further cycle can begin.

By changing the pressure difference between the pressure sources 20 and 22, both the time and the amount of fuel to be injected can be determined. The exact time of the fuel injection through the nozzle tip 14 is determined by the opening time at which the needle piston begins to open. The amount of fuel to be injected is determined by the pressure force of the spring and the pressure difference between the pressure sources 20 and 22 and limited by the completion of the fuel connection between the channels 48 and 52. Since the needle piston 66 begins its downward movement in dependence on the downward movement of the control piston after the Spring 74 compressed to a predetermined value and before a pressure drop at interface 70 has been sensed, the fuel to be injected into a combustion chamber can be controlled much more accurately.

Claims (5)

1. Fuel injection nozzle having a needle piston (66) arranged in a first cylinder chamber (36), the needle piston being provided with a valve needle for opening and closing an injection port and being movable from a valve closing position by the injection pressure, with accompanying tensioning of a spring (74), by an amount corresponding to the opening travel into a valve opening position, and having a control piston (58) which is slidably arranged in a second cylinder chamber (34), is in the end position remote from the needle piston (66) when the needle piston (66) is in the valve closing position, is supported against the spring (74), and controls a fuel duct (52) leading to the first cylinder chamber (36) into the zone between the needle piston (66) and the valve port, the fuel duct (52) being connected to a fuel pressure source (22) in the said end position remote from the needle piston, and, in the valve opening position, in order to initiate the valve closing movement, tensions the spring (74) by a further amount on its adjusting movement towards the needle piston (66) and in so doing isolates the fuel duct (52) from the fuel pressure source, characterised in that pressure is applied to the control piston (58) on the side remote from the needle piston from a second pressure source, a control pressure source (20), and from the first, fuel pressure source on the side close to the needle piston, and the pressure of the fuel pressure source and the pressure of the control pressure source are controllable for initiating and carrying out the valve opening and closing movements, the second cylinder chamber (34) being connectable for pressure relief to a reservoir (24) in that section of the chamber to which the control pressure can be admitted.

2. Fuel injection nozzle according to claim 1, characterised in that a duct (64) is provided in the control piston (58) which connects the fuel duct (52) to another duct (48) leading to the fuel pressure source (22) in the end position of the control piston remote from the needle piston (66).

3. Fuel injection nozzle according to claim 2, characterised in that the duct (64) in the control piston (58) is in the form of an annular duct.

4. Fuel injection nozzle according to one or more of the preceding claims, characterised in that the valve opening position of the needle piston (66) is defined by a retaining ring (76).

5. Fuel injection nozzle according to one or more of the preceding claims, characterised in that the second cylinder chamber (34) is provided with a relief port (54) which is opened from that side of the control piston (58) which is remote from the needle piston on or after the interruption of the connection of the fuel duct (52) with the fuel pressure source (22).

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