WO2005045233A1

WO2005045233A1 - Fuel injection valve for internal combustion engines

Info

Publication number: WO2005045233A1
Application number: PCT/DE2004/001811
Authority: WO
Inventors: Markus Ohnmacht; Wolfgang Stoecklein; Holger Rapp; Andreas Koeninger; Andreas Rau
Original assignee: Robert Bosch Gmbh
Priority date: 2003-10-06
Filing date: 2004-08-13
Publication date: 2005-05-19
Also published as: DE10346212A1

Abstract

Disclosed is a fuel injection valve comprising a housing (1) within which a supply chamber (12) is embodied. A valve needle (18) is disposed in a longitudinally movable manner inside said supply chamber (12). The valve needle (18) cooperates with a valve seat (20) as a result of the longitudinal movement thereof so as to open and close at least one injection port (22). A feeding duct (10) is configured inside the housing (1). The supply chamber (12) can be filled with fuel via said feeding duct (10) such that the fuel is delivered to the injection ports (22) through an annular space (15) which is embodied between the wall of the supply chamber (12) and the valve needle (18) when the injection ports (22) are open. A throttle point (30) which forms the smallest cross-section of the fuel flow from the feeding duct (10) to the injection ports (22) via the annular space (15) is configured within the feeding duct (10).

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 published patent application DE 100 24 703 AI. Such a fuel injection valve has a housing with an inlet space in which a valve needle is arranged to be longitudinally displaceable. Through its longitudinal movement, the valve needle interacts with a valve seat and thereby opens and closes at least one injection opening, which is the injection of

Controls fuel from the inlet chamber into the combustion chamber. The fuel is supplied to the inlet space via an inlet channel and flows through the annular space, which is formed between the wall of the inlet space and the valve needle, in the direction of the injection openings when the valve needle has lifted off the valve seat.

The known fuel injection valve is a so-called stroke-controlled system, in which a high fuel pressure is always present in the inlet space. The valve needle is acted upon by the fuel pressure in a control chamber and thereby experiences a closing force which is countered by an opening force which is caused by the

Fuel pressure in the inlet area acts on the valve needle. By changing the pressure in the control room, the valve needle opens or returns to its closed position.

For proper functioning, it is essential to throttle the fuel flow from the inlet channel to the injection openings. With an unthrottled fuel flow, it is not possible to achieve a closing speed of the valve needle sufficient for the required quantity accuracy. By lifting the valve needle from the valve seat, additional areas of the valve needle are acted upon by the fuel pressure in the inlet space, resulting in a Leads to an increase in the hydraulic opening force acting on the valve needle. If the inflow is not throttled, this additional opening force increases when the valve needle is fully open to the level of the maximum possible hydraulic closing force, so that, starting from this state, only a very slow closing speed can be achieved. However, a slow closing speed leads to a strong, undesirable spread of the closing time and thus also the injection quantity from item to item and from stroke to stroke. In the known fuel injection valve, the valve needle is guided with a central guide area in the inlet space, the fuel flow to the injection openings being ensured by side grindings on the valve needle. The flow cross-section of these cuts is selected so that there is sufficient throttling of the fuel flow.

However, the known fuel injection valve has the disadvantage that the injection characteristic of the injection valve depends very sensitively on the size of the throttles that are formed by the cuts on the valve needle. Even very small manufacturing tolerances in this area lead to a change in the injection behavior, which leads to a large scatter from the injection nozzle to the injection nozzle and thus to an uneven injection behavior in the different pistons of the internal combustion engine. In addition, a small passage cross section in the area of the ground sections has the disadvantage that this leads to pressure fluctuations in the inlet space when the fuel injection valve closes. Since the passage cross section in the area of the ground sections is relatively small, the fuel must have a high speed in this area in order to supply a sufficient amount to the injection openings. The resulting kinetic energy of the fuel in the area of the bevel is converted into compression work when the valve needle closes, which ultimately leads to pressure vibrations in the fuel column between the wall of the inlet space and the valve needle. Such pressure vibrations lead to a slight elastic deformation of the housing and thus to one

Movement of the valve needle on the valve seat, which leads to a disproportionately high wear in this area over time.

Furthermore, throttling in the area of the bevels takes place to a large extent due to wall friction effects due to the small gap height and is therefore strongly depends on the viscosity of the fuel. This creates an undesirable influence of the temperature and the type of fuel on the valve needle dynamics and thus on the injection quantity.

Advantages of the invention

The fuel injection valve according to the invention with the characterizing features of patent claim 1 has the advantage over the fact that the fuel injection valve is relatively insensitive to manufacturing tolerances and has less wear in the area of the valve seat. In addition, the injection behavior is insensitive to temperature fluctuations and fuel-viscosity fluctuations. For this purpose, a throttle point is formed on the inlet channel, which feeds fuel into the inlet chamber, which represents the smallest flow cross-section with respect to the fuel flow from the inlet channel to the injection openings. This allows the grindings on the

Passage cross-section formed larger, which significantly reduces the sensitivity to manufacturing tolerances and there leads to a reduction in the kinetic energy of the fuel. The latter in turn leads to a reduction in pressure vibrations and thus wear on the valve seat.

The dependent claims enable advantageous refinements of the subject matter of the invention. In a first advantageous embodiment, the flow cross section at the passage cross section, which is formed in the filling area of the valve needle, is two to ten times larger than the flow cross section at the throttle point. Such dimensioning has proven to be advantageous in the experiment and ensures that the advantages mentioned above occur.

In a further advantageous embodiment, the passage cross section in the guide region of the valve needle is formed by two to six cuts on the valve needle, which are preferably arranged uniformly distributed over the circumference. Depending on the required flow resistance, the passage cross-section can be adjusted via the number of cuts, without the mechanical stability of the valve needle suffering. In a further advantageous embodiment, the passage cross section on the valve needle is dimensioned such that the kinetic energy of the fuel when the valve needle is placed on the valve seat only triggers weak pressure vibrations in the annular space, that is to say in the inlet space, which do not cause wear on the valve seat. If the kinetic energy in the area of the passage cross-section is low enough, the intensity of the pressure vibrations remains below a critical threshold, which does not cause any noteworthy deformation of the housing and therefore also no additional wear.

drawing

In the drawing, an exemplary embodiment of the fuel injection valve according to the invention is shown. It shows

1 shows a longitudinal section through an inventive fuel injection valve and

Figure 2 shows a cross section through the fuel injector along the line labeled II-II.

Description of the embodiment

FIG. 1 shows a longitudinal section through a fuel injection valve according to the invention. The fuel injection valve has a housing 1, which comprises a valve body 2, a throttle disc 3 and a holding body 5, which are pressed against one another in this order by a clamping nut 7. An inlet chamber 12 is formed in the valve body 2, which essentially has the shape of a stepped bore. The inlet chamber 12 is delimited at its end on the combustion chamber side by a conical valve seat 20, from which a plurality of injection openings 22 emanate, which open into the combustion chamber of the internal combustion engine in the installed position of the fuel injection valve. A piston-shaped valve needle 18 is arranged in the inlet space 12 and is guided in a central guide section 19 on the wall of the inlet space 12. The valve needle 18 has at its end on the valve seat side an essentially conical valve sealing surface 23 with which it cooperates with the valve seat 20 for opening and closing the injection openings 22. An annular space 15 is formed between the valve needle 18 and the wall of the inlet space 12, through which the fuel detects the injection Openings 22 flows. The inlet chamber 12 is filled via an inlet channel 10 with fuel under high pressure, which is formed in the holding body 5 and in the throttle disc 3 and the other end of which is connected to a high-pressure fuel source, not shown in the drawing.

At its end facing away from the valve seat, the valve needle 18 is surrounded by a sleeve 24 which, together with the throttle disk 3, delimits a control chamber 40 which is connected to the inlet channel 10 via an inlet throttle 35. Between the sleeve 24 and a support ring 26, which is supported on a shoulder of the valve needle 18, a closing spring 28 is arranged under pressure, which presses the sleeve 24 against the throttle disk 3 on the one hand and on the other hand a closing force on the valve needle 18 in the direction of the valve seat 20 exercises. As a result, the valve needle 18 is held in contact with the valve seat 20 in the absence of further forces, so that in this case, for example when the internal combustion engine is switched off, the injection openings 22 remain closed.

A control valve 32 is formed in the holding body 5 and comprises a control valve member 33 in a control valve chamber 34. The control valve chamber 34 is connected to the control chamber 40 via an outlet throttle 37 and, moreover, to the inlet chamber 12 via an additional throttle 38. The control valve member 33 is moved longitudinally via an actuator (not shown in the drawing) and thus connects the control chamber 34 to a leakage oil chamber 41 is formed in the holding body 5 and in which there is always a low fuel pressure. If the control valve member 33 is in its position facing away from the valve needle 18, the inflow of the control valve chamber 34 to the leakage oil chamber 41 is interrupted while the additional throttle 38 is opened. If, on the other hand, the control valve member 33 is in contact with the throttle disk 3, the additional throttle 38 is closed and the connection to the leakage oil chamber 41 is opened. The connection of the control valve chamber 34 to the control chamber 40 always remains open.

Figure 2 shows a cross section through the fuel injection valve along the line II-II. On the guide area 19 of the valve needle 18, four bevels 44 are formed, which form four individual channels between the wall of the inlet space 12 and the valve needle 18, which together represent a passage cross section 46. The bevels 44 are designed so that the passage cross section 46 only forms a low flow resistance for the fuel flowing into the injection openings 22. In order to throttle the fuel flow from the inlet channel 10 through the inlet space 12 and the passage cross section 46 to the injection openings 22, a throttle point 30 is arranged in the throttle disc 3, which represents the smallest flow cross section for the entire fuel flow. Except for the other unavoidable flow losses, the throttling of the fuel flow takes place exclusively at the throttle point 30, which has a flow cross-section that is 2 to 10 times smaller than that of the passage cross-section 46.

The fuel injection valve according to the invention functions as follows: At the beginning of the injection, the control valve member 33 is in its first switching position, in which the inflow from the control chamber 34 to the leakage oil chamber 41 is interrupted. About the inlet throttle 35 and the additional throttle 38 prevails in the control valve chamber 34 and in the control chamber 40, the same high fuel pressure as in the inlet channel 10 and in

Inlet chamber 12. If an injection is to take place in which only a small amount of fuel is to be introduced into the combustion chamber, for example for a pre-injection, the actuator is activated and the control valve member 33 comes into contact with the throttle disk 3. This turns the additional throttle 38 are closed and the access from the control valve chamber 34 to the leak oil chamber 41 is opened. The

Pressure in the control valve chamber 34 and thus also in the control chamber 40 then drops because more fuel flows out of the control chamber 40 via the outlet throttle 37 than can flow in via the inlet throttle 35. The hydraulic force on the end of the valve needle 18 facing away from the valve seat is reduced, so that the valve needle 18, driven by the hydraulic pressure on the pressure shoulder 16, lifts off the valve seat 20. Since the valve sealing surface 23 is now acted upon by the fuel of the inlet space 12, there is an additional hydraulic opening force directed away from the valve seat 20, which causes an additional acceleration of the opening movement of the valve needle 18. In order to limit this increase in force, a throttle point 30 is formed in the throttle disk 3, which prevents fuel from flowing into the inlet space 12 too quickly. The pressure increase in the area of the valve sealing surface 23 is therefore less steep and only causes a relatively slow increase in the opening force. Since only a very small amount of fuel is to be injected, the control valve 32 is actuated again before the valve needle 18 abuts the throttle valve. disc 3 is. The control valve member 33 again moves away from the throttle disc 3 and closes the connection of the control valve chamber 34 with the leakage oil chamber 41. As a result, the pressure in the control chamber 40 increases via the inlet throttle 35 and the inlet throttle 38, which additionally fuel via the outlet throttle 37 in the control chamber 40 brings very quickly back on and causes a closing force on the valve needle 18, which brakes its opening movement and accelerates it again in the direction of the valve seat 20 until it sits again on the valve seat 20 and closes the injection openings 22.

The hydraulic closing force that acts on the valve seat

Front side of the valve needle 18 acts to reach a maximum of the area of the front side multiplied by the pressure of the fuel in the control chamber 40, which corresponds to the pressure in the inlet channel 10. If the fuel flow between the inlet duct 10 and the valve seat 20 is not throttled, the hydraulic opening force which acts on the valve needle 18 also has this value when the injection openings 22 are fully open. As a result, only the relatively low biasing force of the closing spring 28 would be available as the resulting closing force. By throttling the fuel flow at the throttling point 30, the hydraulic opening force on the valve needle 18 is slightly reduced and the resulting closing force is increased. This results in a significantly higher closing speed of the valve needle 18 and thus a more precisely defined closing time of the injection valve.

In the area of the connections 44, the fuel is in motion as a result of the injection process, as in the entire inlet space 12, and has a certain kinetic energy. After the injection openings 22 have been closed, the fuel column which is located in the annular space 15 is braked abruptly, which converts the kinetic energy into compression work and finally leads to pressure oscillations in the annular space 15. Due to the relatively large passage cross section 46 in the annular space 15, which is approximately 2 mm ² , the kinetic energy is in

However, the area of the bevels 44 is so small that the pressure vibrations do not lead to any significant expansion of the valve body 2 and thus to no additional wear on the valve seat 20. In addition to the formation of the throttle point 30 on the throttle disc 3, it can also be provided that the throttle point 30 is formed further upstream in the inlet channel 10, depending on which position is advantageous in terms of flow and production technology. It can also be provided that instead of four grindings 44 in the guide area 19 two, three, five or six grindings 44 are provided which provide a corresponding passage cross section 46.

Alternatively, it can also be provided to replace the bevels 44 on the guide section of the valve needle 18 by corresponding recesses on the wall of the inlet space 12, which enable the fuel flow. In this case it is

Guide region 19 of the valve needle 18 is simply cylindrical.

Claims

Expectations

1. Fuel injection valve for internal combustion engines with a housing (1) in which an inlet chamber (12) is formed, in which a valve needle (18) is arranged to be longitudinally and displaceably movable by its longitudinal movement with a valve seat (20) for opening and closing at least one injection opening (22) cooperates, and with an inlet channel (10) formed in the housing (1), via which the inlet space (12) can be filled with fuel in such a way that the fuel when the injection openings (22) are open through an intermediate wall of the inlet space (12) and the valve needle (18) designed annular space (15) flows to the injection openings (22), characterized in that a throttle point (30) is formed in the inlet channel (10), which has the smallest flow cross section of the fuel flow from the inlet channel (10 ) through the annular space (15) to the injection openings (22). 0

2. Fuel injection valve according to claim 1, wherein the valve needle (18) is guided in a central guide section (19) in the inlet space (12) and on the central guide section (19) of the valve needle (18) a passage cross section (46) is provided through which the fuel flows to the at least one injection opening (22). 5

3. Fuel injection valve according to claim 2, wherein the flow cross section at the passage cross section (46) is 2 to 10 times larger than the flow cross section at the throttle point (30).

4. Fuel injection valve according to claim 2, in which the passage cross section (46) is formed by cuts (44) on the guide section (19) of the valve needle (18) 0.

5. Fuel injection valve according to claim 4, in which two to six grindings are provided on the guide section (19) of the valve needle (18), which are arranged uniformly distributed over the circumference of the valve needle (18).

6. Fuel injection valve according to claim 2, wherein the passage cross section 5 (46) on the guide section (19) is formed by recesses on the wall of the inlet space (12).

7. The fuel injector according to claim 2, wherein the flow cross section at the passage cross section (46) is dimensioned such that the kinetic energy of the fuel when the valve needle (18) is placed on the valve seat ϊ 0 (20) only such pressure vibrations in the annular space (15) triggers that do not cause wear on the valve seat (20).

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