EP3580447B1 - Fuel injection valve - Google Patents

Description

The invention relates to a fuel injection valve for the intermittent injection of fuel into the combustion chamber of an internal combustion engine.

Such fuel injection valves are used in fuel injection systems in which fuel is preferably injected directly into the combustion chambers of self-igniting high-speed internal combustion engines, the injection taking place under high pressure. For this purpose, the fuel is conveyed from a fuel tank by a high-pressure fuel pump, compressed to high pressure and conveyed into a so-called rail, which serves as a store for the compressed fuel. Several lines, which are used to supply the fuel injection valves, extend from this high-pressure fuel reservoir.

The fuel injection valves currently used work according to the servohydraulic principle, ie they contain a nozzle needle which is arranged longitudinally displaceably in the high-pressure chamber of the fuel injection valve and which opens or closes one or more injection openings through its longitudinal movement. The The movement of the nozzle needle and thus the start and end of each injection are controlled hydraulically. A control room filled with fuel is available for this purpose. The high pressure fuel exerts pressure on the nozzle needle and presses it against a nozzle seat by means of the hydraulic closing force applied in this way, the pressure here also being applied via a needle closing spring, which already exerts pressure on the nozzle needle if there is no hydraulic pressure is available .. Via a control valve, the pressure exerted on the upper side of the nozzle needle can be reduced so that it lifts off the nozzle seat into its open position and thus releases the injection opening again.

In the known fuel injection valves, corresponding control valves or control devices are used to open and close the injection valve hydraulically with the required force via the nozzle needle when an electrical actuator, for example a piezo or solenoid, is operated. The following embodiments are basically known.

In a 2/2-way control device, the electric actuator releases an outlet throttle via a pilot valve. The pressure reduction in the control chamber causes the nozzle needle to open. When the pilot valve is closed, the control chamber is filled via an inlet throttle and the nozzle needle closes again.

In the case of a 3/2-way control direction, an electrical actuator also releases a discharge throttle via a pilot valve. The pressure reduction in the control room opens the nozzle needle. When the pilot valve is closed and the control device is closed via the inlet throttle, however, a further fuel channel is activated, which fills the control chamber more quickly.

A generic fuel injection valve is from the EP 1991773 B1 known. A 3/2-way control device is implemented here. The known control device is constructed in several parts and has a control valve with a valve insert guided in a valve guide. A discharge throttle is arranged in the valve insert, which permanently connects the areas of the control room that are divided by the control valve. With this design, fuel can be permanently exchanged between the two areas of the control chamber divided by the control valve via the outlet throttle.

The object of the present invention is to develop a generic fuel injection valve in such a way that the hydraulic efficiency is improved during the intermittent injection of the fuel into the combustion chamber and that the opening and closing of the nozzle needle can take place more quickly than in the prior art.

According to the invention, this object is achieved by the combination of the features of claim 1. Accordingly, a fuel injection valve for the intermittent injection of fuel into the combustion chamber of an internal combustion engine is proposed with a housing which has a high pressure chamber which is connected to a high pressure inlet and a low pressure chamber, furthermore with a nozzle needle which is longitudinally movable in the high pressure chamber and which interacts with a nozzle seat a connection of the high pressure chamber with an injection opening opens and closes through its longitudinal movement, the nozzle needle being acted upon by a compression spring with a closing force directed in the direction of the nozzle seat and the compression spring being supported on one side on a spring sleeve in which the nozzle needle is in its free end is guided, further with a limited by the spring sleeve and by the upper end of the nozzle needle control chamber, which can be filled with fuel under pressure and thus exerts a controlled closing force on the nozzle needle, also with a control chamber orderly control valve that divides the control chamber into a first and a second control chamber, the control valve consisting of a valve insert guided in a valve guide and with an outlet throttle being arranged in the valve guide, which is connected to the first control chamber on one side and the other is connected to the second control chamber, wherein the connection formed by the outlet throttle between the first control chamber and the second control chamber can be temporarily interrupted in a targeted manner.

Preferred embodiments of the solution according to the invention emerge from the subclaims that follow the main claim.

Accordingly, the connection formed by the outlet throttle can be interrupted by closing the outlet throttle by means of a switching element.

According to a particularly preferred embodiment of the invention, the switching element consists of a ball arranged in the outlet throttle. This can advantageously consist of steel or ceramic.

According to another alternative advantageous embodiment of the invention, the switching element can also be a slide with a cone, a cylinder or a plate.

To improve the switching mechanism, the switching element provided in each case can be held by a pretensioned spring in a sealing seat provided in the outlet throttle. This enables the desired switching characteristic to be implemented particularly well.

According to a further advantageous embodiment of the invention, the second control chamber can be partially delimited by a seat plate which is connected to the low-pressure chamber via a throttle bore that can be closed in a controlled manner. The throttle bore can be closed by an armature arranged in the low-pressure chamber, the armature being able to be lifted off the throttle bore in a controlled manner by means of an electrical actuator against the bias of the spring. This armature represents the so-called pilot valve, the actuation of which controls the fuel injection valve.

According to a particularly advantageous embodiment, the valve insert can be designed in the shape of a mushroom.

The valve guide furthermore advantageously has an inlet throttle with the supply of fuel under high pressure into the second control chamber.

Furthermore, the valve guide can have at least one diagonally arranged bore, via which the first control chamber can be connected to the high-pressure chamber for the supply of fuel under high pressure. It is particularly advantageous to provide two bores arranged diagonally or offset by 120 °.

The valve guide and the valve insert can advantageously be guided in the spring sleeve in a longitudinally displaceable manner. This creates a particularly compact design.

The functioning of the fuel injection valve according to the invention is as follows:
In the initial state, when the pilot valve is closed, i.e. when the throttle bore is closed and the outlet throttle is blocked at the same time, all pressure chambers have a balanced pressure level in the stationary state, which corresponds to the system pressure. The advantageously mushroom-shaped valve insert is in its lower stop position, so that the two-part control chamber is connected to the high-pressure chamber through the open control valve. The switching element, which is preferably designed as a ball, closes the connection formed by the outlet throttle between the first control chamber and the second control chamber either by its own force of gravity or, in the version with the compression spring, with corresponding spring assistance.

If the pilot valve now opens, ie if the armature is lifted from the throttle bore, the pressure level in the second control chamber first drops as the fuel flows off through the throttle bore. Although fuel flows through the inlet throttle, it cannot prevent a pressure drop in the second control chamber. The emerging The pressure gradient from the first to the second control chamber means that the valve insert is now moved into its upper stop position and thus closes the inlet from the high-pressure chamber. Due to the simultaneous interruption of the connection formed by the outlet throttle between the first and second control chamber, this process is accelerated since the pressure is first reduced in the second control chamber. However, the switching element, for example the ball, is then also displaced from its closed position on the conical seat and fuel flows continuously from the first control chamber via the second control chamber. The pressure drop in the first control chamber reduces the closing force of the nozzle needle on the nozzle seat until the fuel infiltrates the needle seat surface, so that the nozzle needle opens. The nozzle needle then performs its opening stroke, which is maintained by the pressure difference between the high pressure chamber and the control chamber. The nozzle needle would now carry out an opening stroke until it rests against the upper needle stop on the valve insert. This attachment point is designed in such a way that it is never reached in normal operation in engine operation and is therefore not relevant.

Closes the pilot valve, so the armature closes the throttle opening. The continuously existing fuel flow from the high pressure chamber via the inlet throttle ensures the pressure increase in the second control chamber. Immediately after the pressure rise, the reversing pressure gradient, which now sets in from the second control chamber to the first control chamber, acts as a closing force on the switching element provided according to the invention, which is preferably designed as a ball, so that the outlet throttle between the first control chamber and the second control chamber is interrupted or blocked becomes. Closing the outlet throttle supports the faster pressure increase in the second control chamber, so that the valve insert with the switching valve seat opens earlier and releases a large cross section for the fuel inlet from the high-pressure chamber. The pressure in the first control chamber now increases rapidly up to the system pressure level, which reduces the resulting opening force on the nozzle needle to zero. The fast closing process of the nozzle needle now takes place through the force of the needle spring alone. The nozzle seat seals and the injection is ended.

Due to the temporary interruption of the connection between the first control chamber and the second control chamber by the discharge throttle, which is provided according to the invention, the switching times can be shortened, which leads to a better overall function and in particular an improvement in the hydraulic efficiency. The injection process begins and ends earlier. In this way, in the case of multiple injections, the interval between two injections can be shortened.

Further advantages of the solution according to the invention are that a rapid opening of the nozzle needle ensures an earlier build-up of the injection jet, which results in improved combustion in the combustion chamber. The faster opening of the nozzle needle can be used for shorter injection intervals, especially with multiple injections.

The faster closing of the nozzle needle can also be used for shorter injection intervals for multiple injections. The outlet and inlet throttles can be designed for smaller flows. This in turn reduces the fuel outflow during injection via the discharge throttle, so that the hydraulic efficiency of the entire common rail system is improved. A higher hydraulic efficiency also reduces the fuel consumption of an internal combustion engine.

Figur 1:

einen Längsschnitt durch ein erfindungsgemäßes Kraftstoffeinspritzventil,

Figur 2a, b:

eine Detaildarstellung des Kraftstoffeinspritzventils gemäß eines Ausschnitts aus Figur 1,

Figur 3a-c:

weitere Detaildarstellungen gemäß dem Längsschnitt durch das Kraftstoffeinspritzventil entsprechend Figur 1 in unterschiedlichen Arbeitspositionen und

Figur 4:

den zeitlichen Verlauf der Einspritzrate unter Verwendung eines erfindungsgemäßen Einspritzventils im Vergleich zu einem herkömmlichen Einspritzventil.

Further features, details and advantages of the invention are explained in more detail using an exemplary embodiment shown in the drawing. Show it:

Figure 1:

a longitudinal section through a fuel injection valve according to the invention,

Figure 2a, b:

a detailed representation of the fuel injection valve according to a section Figure 1 ,

Figure 3a-c:

further detailed representations according to the longitudinal section through the fuel injection valve Figure 1 in different working positions and

Figure 4:

the time course of the injection rate using an injection valve according to the invention in comparison with a conventional injection valve.

In Figure 1 a fuel injection valve according to the invention is shown schematically in longitudinal section. The fuel injection valve comprises a housing 10, which is connected to a nozzle 14 via a nozzle clamping nut 12. On the opposite side, the housing 10 is connected to an electrical connection wedge 18 via a closure cap 16. A high-pressure chamber 20 is formed in the interior of the housing 10.

As in Figure 1 shown, the fuel injection valve is divided into a high pressure area and a low pressure area. The high-pressure region 20 is delimited by a nozzle seat 22 at its end on the combustion chamber side. In the high pressure area 20, a nozzle needle 24 is arranged to be longitudinally displaceable. This interacts with the nozzle seat 22 to open and close at least one injection opening 26, which is formed in the nozzle 14 facing the combustion chamber. The nozzle needle 24 is guided at its end facing away from the nozzle seat in a spring sleeve 28, a compression spring 32 being arranged under compressive prestress between the spring sleeve 28 and a disc 30 placed on a shoulder of the nozzle needle. This compression spring on the one hand presses the nozzle needle 24 against the nozzle seat 22. On the other hand, it presses the spring sleeve 28 against a control valve 34. The multi-part control valve 34 is supported on a seat plate 36.

The high-pressure chamber 20 can be filled with fuel at high pressure via a high-pressure connection 25, not shown in detail here, which fuel has been compressed by a high-pressure pump not shown in the drawing. This high fuel pressure prevails in the entire high-pressure chamber 20 and has a hydraulic effect Force on the nozzle needle 24, which by far exceeds the force of the closing spring 32. To generate a counterforce necessary for the longitudinal movement of the nozzle needle 24, the nozzle needle delimits a first control chamber 38 with its end face facing away from the nozzle seat, which is laterally delimited by the spring sleeve 28 (cf. Figure 3 ). The side of the first control chamber 38 opposite the nozzle needle 24 is delimited by the two-part control valve 34. This control valve 34 consists of a mushroom-shaped valve insert 40 and an annular valve guide 42. Both the valve insert 40 and the valve guide 42 are each arranged in the spring sleeve 28, as shown in FIG Figure 3 a can be seen. The valve insert 40 is guided in a longitudinally displaceable manner in the valve guide 42. The valve guide 42 rests on the seat plate 36 and, together with the valve insert 40 and the valve guide 42, encloses a second control chamber 44. This second control chamber 44 opens into a throttle bore 46 which can be closed in a controlled manner via an armature 48 (cf. Figure 3 a, b, c ). The armature is located on the low pressure side of the fuel injector, as can be seen from the Figure 1 results. Fuel emerging from the throttle bore 46 is discharged from the housing 10 in the low-pressure region via a leakage oil connection, also not shown here.

The armature 48 is acted upon by a spring 50 in the direction of the throttle bore 46. In the resting state, the armature 48 closes the throttle bore tightly due to the spring force of the compression spring 50. The armature 48 can be lifted from the throttle bore 46 by means of an electromagnet against the spring force of the compression spring 50.

As previously stated, the control valve 34 is designed in two parts in the exemplary embodiment shown here. It consists of the mushroom-shaped valve insert 40. This has a bore 54, as in FIG Figure 3 shown.

The valve guide, in which the valve insert is guided in a longitudinally displaceable manner, has an inlet throttle 56 and an outlet throttle 58. The inlet throttle connects the high-pressure chamber 20 to the second control chamber 44. The outlet throttle 58 connects the first control chamber 38 with the second control chamber 44. The outlet throttle 58 can be closed by a ball 60 (cf. in particular the Figures 2 and 3 ). According to the illustration Figure 3c the valve guide 42 also has two diametrically opposite, diagonally arranged bores 62 through which fuel can flow.

The function of the fuel injection valve according to the invention is as follows. In the de-energized state of the electromagnet 52, the armature 48 closes the throttle bore 46 of the seat plate 36 and prevents the fuel from flowing out of the second control chamber 44 into the leakage area, ie the area in the low-pressure part of the fuel injection valve. Furthermore, the seat plate 36 is pressed against the housing 10 (cf. Figure 1 ). Due to the high surface quality and evenness on the contact surface, a radial seal is provided between the high pressure and low pressure areas (leakage area) and between the high pressure area and the second control chamber 44. This avoids permanent leakage.

As soon as the electromagnet 52 is energized, the armature 48 is lifted from the throttle bore 46 so that fuel flows through the throttle bore 46 of the seat plate 36 from the second control chamber 44 into the low-pressure area and thus generates a pressure drop in the second control chamber 44. The pressure drop creates a pressure difference between the second control chamber 44 and the first control chamber 38.

This pressure difference ensures that the valve insert 40 and the ball 60 are pushed upwards and fuel flows through the outlet throttle 58 in the valve guide 42 from the first into the second control chamber, which in turn creates a pressure equalization between the two control chambers 38, 44 ( compare Figure 3a ). The resulting pressure drop in the first control chamber 38 compared to the high pressure area leads to a lifting of the nozzle needle 24, whereby the injection opening 26 of the nozzle 14 is released and the injector is injected into the combustion chamber, not shown here.

As soon as the electromagnet 52 is no longer energized, the armature 48 closes the throttle bore 46 of the seat plate 36 and the ball 60 is pressed again into a valve seat of the valve guide, not shown here, in order to close the outlet throttle 58.

As a result, the first control space 38 is immediately separated from the second control space 44. The pressure difference between the first and the second control chamber arises due to the fuel flowing in from the high pressure area via the inlet throttle 56 of the valve guide 42 without any further losses due to a flow into the first control chamber 38 (cf. Figure 3b ).

Compared to the conventional three-way valve, with a constant connection between the first and second control chamber, in this control valve 34 according to the invention, the faster pressure build-up in the second control chamber 44 pushes the valve insert 40 down against the spring sleeve 28 earlier. The inlet bores 62 of the valve guide 42 are released and the first control chamber 38 is suddenly filled with fuel from the high pressure area ( Figure 3c ). As a result, the same pressure level is established in the second control chamber 44 as in the first control chamber 38 as in the high pressure area 20. The nozzle needle 24 is pressed back into the nozzle seat 22 by the pressure in the first control chamber 38 and additionally supported by the force of the compression spring 32 and thus terminates the injection into the combustion chamber, not shown here.

In the Figure 2 the closed position of the ball 60 is clearly shown, in which the outlet throttle 35 is closed. In the exemplary embodiment shown here, the ball 60 closes due to gravity. In an alternative embodiment not shown here, the ball can also be supported by a spring, not shown in detail. The representation according to Figure 2b shows the ball 60 in the lifted position. Here, due to the pressure gradient, the ball 60 is moved away from the outlet throttle 58, so that the outlet throttle 58 is released.

In Figure 4 the time course of the injection rate according to the present invention (curve I) is compared with the time course of the injection rate according to the prior art (curve II). The difference is that, according to the prior art, the outlet throttle 58 cannot be closed by a ball 60, so that fuel can flow through the outlet throttle in every state. In the left area of the diagram and in the right area of the diagram, the rising edge and the falling edge are shown enlarged to show the differences in the course more clearly. It is clear here that the start of injection and the end of injection of the embodiment of the present invention (curve I) occur a few microseconds earlier than in the prior art (curve II). As already explained above, this has a great advantage in particular in the case of multiple injection tongues. This means that several injections can be carried out closer in time. Short spray intervals, however, in turn have a great advantage when it comes to meeting emissions from internal combustion engines, since this enables more even burn-up in the combustion chamber.

Claims (11)

1. Fuel injection valve for intermittently injecting fuel into the combustion chamber of an internal combustion engine, comprising
   a housing (10) which comprises a high-pressure chamber (20), which is connected to a high-pressure inlet for fuel, and a low-pressure chamber,
   an injector needle (24) that is longitudinally movable in the high-pressure chamber (20), interacts with a nozzle seat (22), and opens and closes a connection of the high-pressure chamber (20) to an injection opening (26) by the longitudinal movement thereof, wherein the injector needle (24) is urged by a compression spring (32) with a closing force directed towards the nozzle seat (22), and wherein the compression spring (32) is supported at one side on a spring sleeve (28) in which the injector needle (24) is guided by its free end,
   a control chamber (38, 44) that is delimited by the spring sleeve (28) and the upper end of the injector needle (24), and can be filled with pressurized fuel and thus exerts a closing pressure on the injector needle (24) in a controlled manner, and
   a control valve (34) that is arranged in the control chamber (38, 44) and divides the control chamber (38, 44) into a first control chamber (38) and a second control chamber (44), wherein
   the control valve (34) consists of a valve insert (40) guided in a valve guide (42), and
   a discharge throttle (58) is arranged in the valve guide (42), which throttle is connected to the first control chamber (38) on one side and to the second control chamber (44) on the other side,
   characterized in that
   the connection formed by the discharge throttle (58) between the first control chamber (38) and the second control chamber (44) can be temporarily interrupted in a targeted manner,
   a lower stop position of the valve insert (40) connects the control chamber (38, 44) to the high pressure chamber (20) by means of an inlet bore (62) arranged in the valve guide (42),
   an upper stop position of the valve insert (40) closes the inlet from the high-pressure chamber (20), and
   an inlet throttle (56) of the valve guide (42) connects the high-pressure chamber (20) to the second control chamber (44).
2. Fuel injection valve according to claim 1, characterized in that the connection formed by the discharge throttle (58) is interrupted by closing the discharge throttle (58) by means of a switching element.
3. Fuel injection valve according to claim 2, characterized in that the switching element is a ball arranged in the discharge throttle (58).
4. Fuel injection valve according to claim 3, characterized in that the ball consists of steel or ceramic.
5. Fuel injection valve according to claim 2, characterized in that the switching element is a slider with a cone, a cylinder, or a plate.
6. Fuel injection valve according to any of claims 2 to 5, characterized in that the switching element is retained in a sealing seat provided in the discharge throttle (58) by a pre-tensioned spring.
7. Fuel injection valve according to any of the preceding claims, characterized in that the second control chamber (44) is delimited in part by a seat plate that is connected to the low-pressure chamber via a throttle hole that can be closed in a controlled manner.
8. Fuel injection valve according to claim 7, characterized in that the throttle hole can be closed by means of an armature arranged in the low-pressure chamber, wherein it is possible to raise the armature from the throttle hole in a controlled manner counter to the pre-tension of a spring by means of an electrical actuator.
9. Fuel injection valve according to any of the preceding claims, characterized in that the valve insert (40) is mushroom-shaped.
10. Fuel injection valve according to any of the preceding claims, characterized in that the valve guide (42) comprises at least one diagonally arranged hole (62), via which the first control chamber (38) can be connected to the high-pressure chamber (20) in order to supply high-pressure fuel.
11. Fuel injection valve according to any of the preceding claims, characterized in that the valve guide (42) and the valve insert (40) are longitudinally movably guided in the spring sleeve (28).

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