WO2005026525A1

WO2005026525A1 - Fuel-injection valve for internal combustion engines

Info

Publication number: WO2005026525A1
Application number: PCT/DE2004/001331
Authority: WO
Inventors: Joachim Boltz
Original assignee: Robert Bosch Gmbh
Priority date: 2003-08-25
Filing date: 2004-06-24
Publication date: 2005-03-24
Also published as: DE10338768A1

Abstract

The invention relates to a fuel-injection valve comprising a hollow needle (17), which co-operates by longitudinal displacement with a valve seat (27) in such a way that is controls the opening of at least one external injection orifice (30). The hollow needle (17) is provided with a pressurised shoulder (22), which is impinged by the fuel pressure in a pressure chamber (24), thus exerting an opening force that is directed away from the valve seat (27) on the hollow needle (17). A control sleeve (40) that lies at least indirectly against the hollow needle can likewise be longitudinally displaced, the end face (45) of said control sleeve (40) that faces away from the hollow needle (17) delimiting a control chamber (55), in which the pressure can be adjusted. A valve needle (20) is positioned in the hollow needle (17) so that it can be longitudinally displaced, said valve needle co-operating with the valve seat (27) to control the opening of at least one internal injection orifice (32). An internal closing spring (48) exerts a closing force on the valve needle (20), said internal closing spring (48) being supported on the control sleeve (40).

Description

Fuel injection valve for internal combustion engines

State of the art

The invention is based on a fuel injection valve for internal combustion engines, as is known from the document DE 102 05 970 AI. Such a fuel injection valve has a hollow needle which, with its end on the combustion chamber side, interacts with a valve seat from which at least one injection opening extends. The longitudinal opening of the hollow needle closes or opens the injection opening, the longitudinal movement of the hollow needle taking place through the interplay of a closing force and an opening force. The opening force is generated hydraulically by pressurizing a pressure surface arranged in a pressure chamber. The closing force is preferably also generated hydraulically, in that a corresponding pressure acts on the end of the hollow needle facing away from the valve seat in a control chamber. The hydraulic closing force can also act indirectly on the hollow needle in that a control sleeve delimits the control chamber, which in turn rests on the hollow needle. In order to adjust the pressure in the control chamber and thus to control the opening of the hollow needle, a control valve is provided through which fuel can be supplied to the control chamber or can be discharged from the control chamber.

In the hollow needle there is also a longitudinally displaceable valve needle which interacts with the valve seat with its end facing the valve seat and thereby controls the opening of at least one further injection opening. The opening force on the valve needle is also generated hydraulically by the pressure in the pressure chamber, while the closing force is exerted by the pressure in a second control chamber. This second control chamber is formed either in the hollow needle or in the control sleeve interacting with the hollow needle. However, the known fuel injection valve has the disadvantage that the closing force on the valve needle and thus the pressure in the second control chamber have to be controlled in a complex manner. Either the second control chamber is also connected to the control valve in such a way that its pressure can be adjusted with the aid of the control valve, or a second control valve is to be provided, which causes additional costs and takes up more installation space. Solclαe constructions are expensive and have to be sealed in many places.

Advantages of the invention

The fuel injection valve according to the invention with the characterizing features of patent claim 1 has the advantage that control of two coaxially guided valve needles is possible in a simple manner and using known and proven control means. For this purpose, the valve needle, which is guided in the hollow needle, is acted upon by a closing force by means of a closing spring, the closing spring being supported on the control sleeve. The closing force is therefore generated exclusively by a closing spring, so that the valve needle can be moved in the known manner by appropriately pressurizing a pressure surface.

Advantageous refinements of the subject matter of the invention are possible through the further claims.

In a first advantageous embodiment, the closing spring is arranged in an inner spring chamber which is formed in the control sleeve and is open towards the valve needle. This configuration is particularly advantageous if this inner spring chamber is connected via an opening in the control sleeve to an outer spring chamber, in which an outer closing spring is arranged and which is connected to a leakage line. In this way, a low fuel pressure is always maintained in both spring chambers, which does not exert any additional, disruptive forces on the valve needles.

In further advantageous refinements, a control valve is provided in the fuel injection valve, with the aid of which the fuel pressure in the control chamber can be set. For this purpose the control valve is either a 3/2 or 2/2 Directional valve designed, the 3/2-way valve has the additional ^' advantage that the pressure build-up is significantly accelerated after the end of the injection and the valve needle closes accordingly quickly. In contrast, a 2/2-way valve is generally simpler in design and correspondingly less expensive.

drawing

In the drawing is an embodiment of the invention. Fuel injector shown. It shows

1 shows a fuel injection valve according to the invention in longitudinal section with schematically illustrated peripheral components and FIG. 2 shows the time course of the needle stroke, injection rate and the force on the valve needle at various injection pressures.

Description of the exemplary embodiment

In Figure 1, an embodiment of the fuel injection valve according to the invention is shown in longitudinal section. The fuel injection valve has a housing 1, which comprises a valve body 3, a control body 5, a throttle disc 7 and a holding body 9, which abut one another in this order and are pressed against one another by a device not shown in the drawing. A bore 15 is formed in the valve body 3, which is delimited at its combustion chamber end by a conical valve seat 27. From the valve seat 27 go outer injection openings 30 and imiere injection openings

32 from which open into the combustion chamber of the internal combustion engine when the fuel injection valve is in the installed position. In the bore 15, a hollow needle 17 is arranged to be longitudinally displaceable and is sealingly guided in a section of the bore 15 facing away from the valve seat. A pressure chamber 24 is formed between the hollow needle 17 and the wall of the bore 15, which extends to the valve seat 27 and which is connected to a high-pressure chamber 11 via an inlet channel 35 running in the housing 1. A predetermined fuel pressure is always maintained in the high-pressure chamber 11, which can be part of a fuel pump or a high-pressure collection chamber, so that this pressure also prevails in the pressure chamber 24 and thus also corresponds to the necessary injection pressure. Starting from the guided section of the hollow needle 17, it tapers towards the valve seat 27 to form a pressure shoulder 22, at the level of which the inlet channel 35 opens into the pressure chamber 24. At its end on the valve seat side, the hollow needle 17 merges into a valve sealing surface 18 with which it connects with the valve seat

27 interacts in such a way that when the hollow needle 17 abuts, the pressure chamber 24 is closed against the outer injection openings 30 and, after lifting off the valve seat 27, fuel flows from the pressure chamber 24 between the valve sealing surface 28 and the valve seat 27 to the injection openings 30 and through them se is injected into the combustion chamber.

A through hole 41 is formed in the control body 5, in which a control sleeve 40 is arranged so as to be longitudinally displaceable. The control sleeve 40 rests with its end on the valve seat side against the hollow needle 17, so that it moves in synchronism with it in the through bore 41. Adjacent to the valve body 3, the through bore 41 is expanded to an outer spring space 37, in which an outer closing spring 47 in the form of a helical compression spring is arranged under prestress. The outer closing spring 47 is supported at one end on a stationary support surface 45 and at the other end on an arx of the control sleeve 40 formed shoulder 44. By prestressing the outer

Closing spring 47 results in a force on hollow needle 17 in the direction of valve seat 27, so that it is held in its closed position in the absence of additional forces, that is to say in contact with valve seat 27.

In the hollow needle 17, a piston-shaped valve needle 20 is arranged so as to be longitudinally displaceable, which has at its end on the valve seat side a valve sealing surface 29 with which the valve needle 20 interacts with the valve seat 27. The valve needle 20 has a pressure surface 23 near the valve sealing surface 29, which is acted upon by the fuel pressure of the pressure chamber 24 when the hollow needle 17 is open and thereby experiences an opening force on the valve needle 20. By lifting the

Valve needle 20 from valve seat 27, the inner injection openings 32 are released, so that if the hollow needle 17 is also lifted off the valve seat 27, fuel is injected into the combustion chamber through the imitation injection openings 32 and at the same time through the outer injection openings 30. At its end facing away from the valve seat, the valve needle 20 merges into a spring plate 50 which is arranged within an inner spring chamber 38 formed in the control sleeve 40. The spring plate 50 can be designed as a separate part or in one piece with the valve needle 20. In the inner spring chamber 38, an inner closing spring 48 is arranged under pressure, which is supported at one end on the spring plate 50 and at the other end on the control sleeve 40. As a result, a closing force directed onto the valve seat 27 is exerted on the valve needle 20, which holds it in its closed position. The inner spring chamber 38 is connected via a connecting bore 42 to the outer spring chamber 37, which is connected via a leakage line 60 to a leak oil chamber, not shown in the drawing. As a result, the pressure in the inner spring chamber 37 and in the outer spring chamber 38 always remains low, preferably to ambient pressure. A driving shoulder 52 is formed in the inner spring space 38, which, when the valve needle 20 and the hollow needle 17 are in the closed position, is at a slight axial distance from the spring plate 50. However, there are

Valve needle 20 and the hollow needle 17 in the open position, the valve needle 20 is carried during the closing movement of the hollow needle 17 and thus the Steuerlαülse 40 by the abutment of the driving shoulder 52 on the spring plate 50 and pressed into its closed position.

The end face 57 of the control sleeve 40 facing away from the hollow needle 17, the through bore 41 and the throttle disk 7 delimit a control chamber 55, the pressure of which exerts a hydraulic force on the control sleeve 40 in the direction of the hollow needle 17. The control chamber 55 is connected to the inlet channel 35 via an inlet throttle 62 and a connecting groove 66 formed in the throttle disk 7, so that fuel always flows into the control chamber 55 via the inlet throttle 62 as long as there is a lower pressure there than in the high-pressure chamber 11 and thus in Inlet channel 35. Control chamber 55 is also connected via an outlet throttle 64 and a control line 69 to a control valve 70, which is also connected to inlet throttle 62 via a further control line 68. Furthermore, the control valve 70 is connected to a leakage line 72, which opens into a leakage oil space, not shown in the drawing, in which there is always a low pressure, preferably ambient pressure. The control valve 70 is designed as a 3/2-way valve, which consequently has two switching positions: in the first switching position shown, the Control line 68 and control line 69 connected to each other while the leakage line 72 is closed. In the second switching position, the leakage line is connected to the control line 69 and thus to the flow restrictor 64, while the control line 68 is closed.

The fuel injector works as follows:

Depending on the performance requirements for the Brerin engine, a more or less high pressure is set in the high-pressure chamber 11. A relatively low pressure, for example in the order of 30 to 40 MPa, is sufficient for a low power requirement. The injection begins by moving the control valve 70 into its second switching position, so that the control chamber 55 is connected to the leakage line 72. As a result, the pressure in the control chamber 55 is reduced below the pressure of the inlet line 35, since the inlet throttle 62 and the outlet throttle 64 are matched to one another in such a way that more fuel flows out of the control chamber 55 than can flow in via the inlet throttle 62. The hydraulic pressure on the pressure shoulder 22 of the hollow needle 17 lifts it off the valve seat 27 and opens the outer injection openings 30. At this low pressure in the pressure chamber 24, the hydraulic force on the pressure surface 23 is not sufficient to open the valve needle 20 against the force of the inner closing spring 48, so that it remains in its closed position, ie in contact with the valve seat 27. To end the injection, the control valve 70 is brought back into its first switching position, in which it connects the two control lines 68, 69 to one another. As a result, the leakage line 72 is closed on the one hand, and on the other hand, fuel flows into the control chamber 55 both via the inlet throttle 62 and via the outlet throttle 64, so that a high fuel pressure is built up again very quickly, which forces the hollow needle 17 into its closed position suppressed.

FIG. 2 shows the course of the needle stroke h, the injection rate R and the force F on the valve needle 20 against time, the column denoted by A denoting the low injection pressure, B a medium and C a high injection pressure. The function described above at low injection pressure corresponds to the diagrams in the A column: The needle stroke h _{a of} the hollow needle 17 rises to a maximum and falls again after actuation of the control valve 70. from until the hollow needle 17 is closed. The injection rate R quickly rises to a plateau, since this is limited not only by the stroke of the hollow needle 17, but also by the diameter of the outer injection openings 30. The closing force Fg on the valve needle 20 is reduced by the moving control sleeve 40, since the inner closing spring 48 is extended. The opening force F _oe still does not reach this closing force, so that the valve needle 20 remains closed. The hollow needle 17 does not move through its greatest possible stroke: by rapidly actuating the control valve 70, the hollow needle 17 remains in a ballistic state and is braked by the pressure in the control chamber 55 which rises again before it can contact the throttle disk 7.

At an average injection pressure in the high-pressure chamber 11 or in the pressure chamber 24, the hollow needle 17 is opened in the manner described above after actuation of the control valve 70. In FIG. 2, the course of the needle stroke h _{a of} the hollow needle 17 is similar to that in example A, but the increase is due to the higher

Pressure in the pressure chamber 24 is steeper. Due to the greater hydraulic force on the pressure surface 23 of the valve needle 20, the valve needle 20 now also opens against the closing force of the inner closing spring 48. The stroke of the valve needle 20 is designated by h [in FIG. In the force diagram of example B in FIG. 2, the opening of the valve needle 20 can be seen in that the opening force F _oe the closing force

Fg reached, which drops as long as the hollow needle 17 is moving. The injection rate R increases suddenly after the valve needle 20 is opened. The injection is terminated as in the case of the low injection pressure, but the valve needle 20 is not only moved by the falling pressure on the pressure surface 23 and the inner closing spring 48, but also by the engagement of the driving shoulder 52 on the spring plate 50.

At a high injection pressure, which corresponds to example C in FIG. 2, the hollow needle 17 and the valve needle 20 open practically simultaneously, since immediately after the hollow needle 17 is lifted off the valve seat 27, a very high pressure is applied to the pressure surface 23 and thus a large force acts on the valve needle 20. At the beginning, the injection rate R still shows a slight increase, which is caused by the opening of the hollow needle 17, but very quickly reaches its maximum value, which is higher than the maximum injection rate of example B due to the high pressure. Instead of designing the control valve 70 as a 3/2 way valve, it can also be provided that it is instead designed as a 2/2 way valve which opens or closes the connection of the control line 69 to the leakage line 72. The control line 68 can be omitted in this exemplary embodiment. The opening function remains the same, but the closing of the valve needle 20 takes place more slowly, since the pressure build-up in the control chamber 55 now only takes place via the inlet throttle 62 and thus takes a little more time.

The control valve is preferably driven with the aid of a piezo actuator, which allows a very short switching time. However, it is also possible to use an electromagnetic control valve 70.

Claims

Expectations

1. Fuel injection valve for internal combustion engines with a hollow needle (17) which, through its longitudinal displacement, interacts with a valve seat (27) in such a way that it controls the opening of at least one outer injection opening (30), and with one formed on the hollow needle (17) Pressure shoulder (22), which is acted upon by the fuel pressure in a pressure chamber (24) and thereby exerts an opening force directed away from the valve seat (27) on the hollow needle (17), and with a control sleeve (40), which is also longitudinally displaceable and at least bears indirectly on the hollow needle (17), the control sleeve (40) delimiting a control chamber (55) with its end face (45) facing away from the hollow needle (17) and the pressure in the control chamber (55) being adjustable, and with one in the hollow needle (17) longitudinally displaceably arranged valve needle (20) which, by interacting with the valve seat (27), controls the opening of at least one inner injection opening (32), characterized in that: ass the valve needle (20) is acted upon by an inner closing spring (48) with a closing force, the inner closing spring (48) being supported on the control sleeve (40).

2. Fuel injection valve according to claim 1, characterized in that the inner closing spring (48) is arranged in an inner spring chamber (38) formed in the control sleeve (40), the imiere spring chamber (38) being open towards the valve needle (20).

3. Fuel injection valve according to claim 1, characterized in that an outer closing spring (47) is provided which is supported at one end in a stationary manner and which rests with its other end on the control sleeve (40) in such a way that a closing force on the Hollow needle (17) is exercised.

4. Fuel injection valve according to claim 3, characterized in that the outer closing spring (47) is arranged in an outer spring chamber (37) which is connected to a leakage line (60).

5. Fuel injection valve according to claim 4, characterized in that the inner closing spring (48) is arranged in an inner spring chamber (38) formed in the control sleeve (40), the inner spring chamber (38) being hydraulically connected to the outer spring chamber (37) is.

6. Fuel injection valve according to claim 1, characterized in that the control chamber (55) via an inlet throttle (62) can be connected to a high-pressure chamber (11) and via an outlet throttle with a leakage line.

7. Fuel injection valve according to claim 6, characterized in that a control valve (70) is provided which is designed as a 3/2-way valve and which is connected to a leakage line (72) in such a way that in the first switching position it is the leakage line (72 ) connects to the outlet throttle (64) and in the second switching position connects the high pressure chamber (11) to the outlet throttle (64) and at the same time closes the leakage line (72), the inlet throttle (62) always remaining connected to the high pressure chamber (11).

8. Fuel injection valve according to claim 6, characterized in that a control valve (70) is provided, which is designed as a 2/2-way valve and which is connected to a leakage line (72) that the control valve (70) in a first switching position the discharge throttle (64) connects to the leakage line (72), while this connection is interrupted in the second switching position of the control valve (70).

9. Fuel injection valve according to claim 7 or 8, characterized in that the control valve (70) is actuated via a piezo actuator.

10. Fuel injection valve according to one of claims 1 to 9, characterized in that the control sleeve (40) and the hollow needle (17) are made in one piece.