WO2003054379A1

WO2003054379A1 - Pump jet unit

Info

Publication number: WO2003054379A1
Application number: PCT/DE2002/004426
Authority: WO
Inventors: Dejan Jovovic; Maximilian Kronberger
Original assignee: Volkswagen Mechatronic Gmbh & Co. Kg
Priority date: 2001-12-07
Filing date: 2002-12-03
Publication date: 2003-07-03
Also published as: EP1451465B1; DE10160080A1; DE50204124D1; EP1451465A1

Abstract

The invention relates to a pump jet unit for the introduction of fuel (10) into the combustion chamber (12) of an internal combustion engine. According to the invention, a defined control of the injection process and the injection pressure is possible with a compact construction, whereby a pressure-limiting and -maintaining valve (34) is provided between a first pressure chamber (28), which may be filled with fuel (10) at a first pressure (p28) from a fuel pump (14-22) and a second pressure chamber (30). The fuel (10) at a second pressure (p30) in the second pressure chamber (30) exerts a closing force on the nozzle needle (26).

Description

description

Pump-nozzle unit

The invention relates to a pump-nozzle unit for supplying fuel into a combustion chamber of an internal combustion engine, with a control and / or regulable fuel pump, a fuel injection nozzle which has a nozzle needle which can be moved back and forth between a closed position and an open position, one first pressure chamber, which can be filled by the fuel pump with fuel under a first pressure, a second pressure chamber, fuel in the second pressure chamber under a second pressure exerting a closing force on the nozzle needle, and a third pressure chamber that communicates with the first pressure chamber , wherein in the third pressure chamber a third pressure fuel exerts an opening force on the nozzle needle.

Pump-nozzle units of this type are used in particular in connection with pressure-controlled injection systems. An essential feature of a pressure-controlled Eirtspritzsyste s is that the fuel injector opens as soon as an opening force that is at least influenced by currently prevailing pressures is exerted on the nozzle needle. Pressure-controlled injection systems of this type are used for fuel metering, fuel conditioning, shaping the course of the injection and sealing the fuel supply against the combustion chamber of the internal combustion engine. With pressure-controlled injection systems, the time course of the volume flow can be controlled in an advantageous manner during the injection. This can have a positive impact on the performance, fuel consumption and pollutant emissions of the engine.

The fuel pump and the fuel injection nozzle are integrated in the generic pump-nozzle units Component trained. At least one pump-nozzle unit is provided for each combustion chamber of the internal combustion engine and is usually installed in the cylinder head. The fuel pump typically comprises a fuel pump piston that can be moved back and forth in a fuel pump cylinder and is driven either directly by a tappet or indirectly by rocker arm of a camshaft of the internal combustion engine. The section of the fuel pump cylinder which usually forms the first pressure chamber can be connected to a low-pressure fuel region via a control valve, fuel being sucked into the first pressure chamber from the low-pressure fuel region when the control valve is open and back into the low-pressure fuel region from the first pressure chamber when the control valve is still open - is pressed. As soon as the control valve is closed, the fuel pump piston compresses the fuel located in the first pressure chamber and thus builds up pressure. It is known to provide the control valve in the form of a solenoid valve. However, solenoid valves usually have a relatively long response time, which is due in particular to the fact that the magnet armature of a solenoid valve cannot be accelerated as quickly as desired due to the inertia forces which are dependent on its mass. Furthermore, the build-up of the magnetic field to generate the attraction force requires time. A pump-nozzle unit equipped with a solenoid valve is known for example from EP 0 277 939 B1.

In order to avoid the problems caused by the use of solenoid valves, it is also known to equip pump-nozzle units with a control valve which is operated piezoelectrically. Such a pump nozzle unit is known for example from DE 198 35 494 AI.

In addition to a main injection quantity, an additional pre-injection quantity and / or an additional quantity during an injection process Introducing post-injection closely into the combustion chamber, it is also known to trigger a plurality of injection pulses which follow one another at short time intervals during an injection cycle. Furthermore, it may be advantageous to regulate the injection pressure by means of injection course shaping in such a way that high pressure peaks and thus hard burns are avoided. For this purpose, an injection profile shaping injector is already known from DE 199 42 846 C1, for example, in which the pressure setting is to be improved by using compensating means.

The invention has for its object to develop the generic pump-nozzle units such that a defined control of the injection process and the injection pressure is made possible in a compact design.

This object is solved by the features of claim 1.

Advantageous refinements and developments of the invention result from the dependent claims.

The pump-nozzle unit according to the invention builds on the generic prior art in that a pressure limiting and holding valve is provided between the first pressure chamber and the second pressure chamber. The pressure limiting and holding valve provided according to the invention makes it possible, in particular, to set the second pressure prevailing in the second pressure chamber in such a way that a closing force which acts on the nozzle needle and is suitable for the respective operating and load conditions of the internal combustion engine results. The closing force counteracts an opening force likewise exerted on the nozzle needle, which depends on the third pressure prevailing in the third pressure chamber. It is thus possible, for example, to set a relatively low second pressure for a pre-injection in the second pressure chamber, so that the nozzle needle is already moved into an opening position when in the third pressure chamber a relatively low third pressure prevailing due to the opening force. While the third pressure in the third pressure chamber initially drops again during or after the pre-injection, the pressure in the second pressure chamber can be built up further, as a result of which the nozzle needle for the subsequent main injection only moves back into the open position when the third pressure has risen to a relatively high value in the third pressure chamber. During the main injection, the second pressure remains in the second pressure chamber due to the pressure limitation and

holding valve almost constant. The level of the pressure, which is kept essentially constant during the main injection, influences the length of the main injection.

In preferred embodiments of the pump-nozzle unit according to the invention it is provided that the pressure limiting and holding valve is actuated by a pressure difference. In this way, actuators assigned to the pressure limiting and holding valve can be omitted, which has a positive effect both in terms of the manufacturing costs and in terms of the required installation space.

In this context, it is preferably further provided that the pressure difference is the difference between the first pressure and the second pressure. The mode of operation is preferably such that the pressure prevailing in the first pressure chamber initially opens the pressure limiting and holding valve, as a result of which the second pressure in the second pressure chamber is increased. The respective opening cross section preferably increases initially with a rising first

Print. As soon as a pressure difference between the first pressure and the second pressure, which can be influenced, inter alia, by the choice of the respective opening cross sections, is reached, the pressure limiting and holding valve is closed, as a result of which the second pressure in the second pressure chamber is essentially constant, for example, during a main injection can be held. In many cases it is advantageous if the pressure limiting and holding valve is designed as a 2/3 valve. A 2/3 valve has two connections, one of which can be assigned to the first pressure chamber and one to the second pressure chamber in the present context. Furthermore, a 2/3 valve has three different switching states. Transferred to the present context, these three switching states can be assigned in particular to the closed valve, a valve opening with an opening cross section and an unstable valve opening with an opening cross section.

Regardless of the special configuration of the pressure limiting and holding valve, it is preferably provided that the pressure limiting and holding valve has a first working position in which it is closed.

In this context, it is considered to be particularly advantageous if it is provided that the first working position is a rest position forced by spring forces.

It is further preferred that the pressure limiting and holding valve has a second working position with an opening cross section.

In this context, it is considered advantageous if it is additionally provided that the pressure limiting and holding valve has an unstable third working position with an opening cross section. An unstable working position is to be understood here in particular as a position that is not a defined intermediate and end position.

Another preferred development of the present invention provides that the pressure limiting and holding valve has a fourth working position, different from the first working position, in which it is closed. It is advantageous that the pressure limiting and holding valve is in the fourth working position when the first pressure exceeds the second pressure by a predetermined value. As soon as the first pressure decreases again, the pressure limiting and holding valve preferably leaves the fourth working position and, in preferred embodiments, returns to the third, the second or the first working position, depending on the amount of the current difference between the first pressure and the second pressure - back.

It is considered particularly advantageous for the pump-nozzle unit according to the invention if it is provided that a first spring is provided in the second pressure chamber, which exerts a closing force on the nozzle needle. Such a known per se first spring ensures, among other things, that the fuel supply ^'relative to the combustion chamber of the internal combustion engine is sealed, when the unit injector is at rest. The closing force exerted by the first spring on the nozzle needle is complemented by the closing force exerted on the nozzle needle by the second pressure in the second pressure chamber during operation of the pump-nozzle unit according to the invention.

It may be advantageous if the first spring is biased differently depending on different working positions of the pressure limiting and holding valve. It can be advantageous if the spring preload before a pre-injection is less than before a skin injection. The respective pretensioning of the first spring is advantageously set via the pressure limiting and holding valve or one or more components assigned to it.

In a particularly preferred embodiment, it is provided that the pressure limiting and holding valve has a valve plate which is connected to a first valve seat. acts, which is provided adjacent to the first pressure chamber. It is considered to be particularly advantageous if at least the portion of the valve plate interacting with the first valve seat is rounded, in particular spherical. In this case, the geometry of the first valve seat is preferably adapted to that of the valve plate.

In this connection, in particular, it is preferably further provided that the pressure limiting and holding valve has a plate which interacts with a stop which is provided adjacent to the second pressure chamber. The plate can for example be disc-shaped. In particularly preferred embodiments of the pump-nozzle unit according to the invention, the valve plate and the plate are formed by separate parts.

In the context explained above, it is further provided in preferred embodiments that the valve plate continues to cooperate with a second valve seat, which is arranged between the first valve seat and the stop. The pressure limiting and holding valve is then preferably closed both when the valve plate lies against the first valve seat and when the valve plate lies against the second valve seat.

In the context explained above, in particular, it is preferably further provided that a complete seal is not achieved when the plate rests on the second valve seat. For this purpose, for example, at least one hole can be provided in the plate. Additionally or alternatively, it is possible to provide grooves or the like on the side of the plate facing the stop. An equivalent effect can be achieved if the stop is equipped with appropriate grooves. The dimensions of the bore or the bores and / or the groove or the grooves are preferably selected in such a way that that they at least do not excessively delay the build-up of pressure in the second pressure chamber.

With regard to the already mentioned first working position, in which the pressure limiting and holding valve is closed, it is preferred that the valve disk rests on the first valve seat in the first working position.

With regard to the second working position, also mentioned above, in which the pressure limiting and holding valve has an opening cross section, it is preferred that the valve plate in the second working position does not rest on the first valve seat and not on the second valve seat, and that the plate in the second Working position is at the ^' stop.

With regard to the already unstable third working position, in which the pressure limiting and holding valve has an opening cross section, it is preferred that the valve plate in the third working position does not rest on the first valve seat and not on the second valve seat, and that the plate in the third working position does not touch the stop.

Finally, with regard to the fourth working position, which already differs from the first working position and in which the pressure limiting and holding valve is also closed, it is preferred that the valve plate rests on the second valve seat in the fourth working position and that the plate does not touch the stop in the fourth working position.

In all embodiments of the pump-nozzle unit according to the invention is preferably provided that the first spring ^'on the plate is supported. Since the plate in the third and fourth working position preferably moves towards the nozzle needle, the first spring is (further) biased depending on the movement of the plate. An High bias of the first spring may be desirable, for example, to increase the opening pressure required for a main injection.

As is known per se, it is also advantageously provided in the pump-nozzle unit according to the invention that the fuel umpe has a fuel pump piston driven by the internal combustion engine. The fuel pump piston can in particular be driven via a camshaft of the internal combustion engine. The drive can take place directly via tappets or indirectly via rocker arms.

In this context, it is preferably also provided that the fuel pump has a control valve with which the first pressure chamber can be completely or partially closed off from a low-pressure fuel region. An open control valve enables fuel to be drawn in, while a closed control valve enables compression of the previously drawn-in fuel and thus pressure build-up.

With regard to the fuel pump, it is preferably further provided that the control valve is operated piezoelectrically. As mentioned at the beginning, a piezoelectrically operated control valve, for example in comparison to a solenoid valve, enables a much more precise and faster control. , ••

The invention is based on the finding that the control, in particular of the nozzle opening pressure, can be improved compared to the prior art by setting a pressure which exerts a closing force on the nozzle needle via a pressure limiting and holding valve. The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments.

Show it:

1 shows a schematic embodiment of the pump nozzle unit according to the invention;

Figure 2 is an enlarged view of the area of the pump-nozzle unit of Figure 1, in which the pressure limiting and holding valve is provided;

Figure 3 is a plan view of an embodiment of the plate;

FIG. 4 shows a schematic detailed view of the pressure limiting and holding valve according to FIG. 2 in its first working position, in which it is closed;

FIG. 5 shows a schematic detailed view of the pressure limiting and holding valve according to FIG. 2 in its second working position, in which it has an opening cross section;

FIG. 6 shows a schematic detailed view of the pressure limiting and holding valve according to FIG. 2 in its unstable third working position in which it also has an opening cross section;

FIG. 7 shows a schematic detailed view of the pressure limiting and holding valve according to FIG. 2 in its fourth working position, in which it is also closed;

FIG. 8 is a curve which illustrates a possible course of the second pressure within the second pressure chamber as a function of the crankshaft angle; FIG. 9 is a curve which illustrates a possible course of the third pressure within the third pressure space as a function of the crankshaft angle; and

Figure 10 is a curve illustrating a possible injection curve depending on the crankshaft angle.

Figure 1 shows a schematic embodiment of the pump nozzle unit according to the invention. The pump-nozzle unit shown for supplying fuel 10 into a combustion chamber 12 of an internal combustion engine has a fuel pump 14-22. A fuel pump piston 14 is movable back and forth in a fuel pump cylinder 16. The fuel pump piston 14 is driven directly or indirectly via a camshaft, not shown, of the internal combustion engine. The compression space of the fuel pump cylinder 16 forms the first pressure space 28. The first pressure space 28 is connected via a fuel line 20 to a piezoelectrically operated control valve 22 known per se. The control valve 22 serves to either close the fuel line 20 or to connect it to a low-pressure fuel region 18 from which fuel 10 can be drawn. In its open rest position, fuel 10 is drawn from the low-pressure fuel region 18 into the first pressure chamber 28 when the fuel pump piston moves upward in relation to FIG. 1. If the control valve 22 is still in its open rest position when the fuel pump piston 14 moves downward with respect to FIG. 1, fuel 10 previously drawn into the first pressure chamber 28 can be pressed back into the low-pressure fuel region 18. When the control valve 22 is actuated, it closes the fuel line 20. As a result, the fuel 10 drawn into the first pressure chamber 28 is compressed when the fuel pump piston 14 moves downward. whereby the first pressure is generated in the first pressure chamber 28. The pump-nozzle unit shown further comprises a fuel injection nozzle, designated as a whole by 24, which has a nozzle needle 26 which can be moved back and forth between a closed position and an open position. The upper end section of the nozzle needle 26 with respect to FIG. 1 has a nozzle needle piston 50 which is guided in a second pressure chamber 30, fuel 10 in the second pressure chamber 30 under a second pressure p ₃ o having a pressure based on the illustration in FIG. 1 downward closing force exerts on the nozzle needle 26. The nozzle needle piston 50 is preferably only so strongly sealed to the second pressure chamber 30, that the second pressure p ₃ is degraded already again o before the start of a new injection cycle. A further closing force, likewise directed downward, is exerted on the nozzle needle 26 by a first spring 36, the first spring 36 being arranged in the second pressure chamber 30 and having its rear end supported on the nozzle needle piston 50. A section of the nozzle needle 26 having a shoulder 58 is from a third pressure chamber

Surround 32, which communicates with the first pressure chamber 28 via a connecting line 48. A third pressure p _{32 is} built up in the third pressure chamber 32 as a function of the throttling action of the connecting line 48 and, if appropriate, further throttling devices (not shown), depending on the first pressure p ₂₈ prevailing in the first pressure chamber 28. The fuel 10, which is under the third pressure p ₃₂ in the third pressure chamber 32, exerts an opening force on the nozzle needle 26 that is directed upward in relation to the illustration in FIG. 1. The nozzle needle 26 assumes its open position as long as a difference between the opening force caused by the third pressure p ₃ and the sum of the closing force generated by the second pressure p ₃₀ and the closing force generated by the first spring 36 exceeds a predetermined value. ₃ p o in the second pressure chamber 30 via the second pressure can hence the nozzle opening pressure can be influenced. To the second pressure To limit and maintain p ₃₀ in the second pressure chamber 30 to appropriate values, a pressure limiting and holding valve 34 is provided between the first pressure chamber 28 and the second pressure chamber 30.

FIG. 2 shows an enlarged representation of the area of the pump-nozzle unit from FIG. 1, in which the pressure limiting and holding valve 34 is provided. In this case, the pressure limiting and holding valve 34 has a valve plate 38, the upper side 60 of which is hemispherical. The upper side 60 of the valve plate 38 is designed to cooperate with a first valve seat 40 provided adjacent to the first pressure chamber 28, which will be explained in more detail later with reference to FIG. 4. The flat underside 62 of the valve plate 38 is designed to cooperate with a second valve seat 46, which will be explained in more detail later with reference to FIG. 7. The valve plate 38 is guided with a game that allows movement up and down based on the representation. At the same time, this play defines the opening cross section of the pressure limiting and holding valve 34 in some position of the valve plate 38. If the diameter of the underside 62 of the valve plate 38 is five millimeters, the play for this purpose can be, for example, in the range from 20 to 100 micrometers. The pressure limiting and holding valve 34 also has a plate 42 which is formed separately from the valve plate 38. The first spring 36 provided in the second pressure chamber 30 is supported on the underside of the plate 42. A shaft 68 extends from the top of the plate 42 and is surrounded by a second spring 56, which is supported both on the valve plate 38 and on the plate 42 and thus, based on the illustration in FIG exerts a directed force on the valve plate 38 and a downward force on the plate 42. The plate 42 is designed to cooperate with a stop 44, which will be explained in more detail later with reference to FIGS. 4 and 5. The plate 42 has a bore 52 and a plurality of grooves 54, the mode of operation of which will be explained in more detail below with reference to FIG. 5.

FIG. 3 shows a top view of an embodiment of the valve plate. It can be seen here that the plate 42 in the embodiment shown has a bore 52 and three grooves 54, the mode of operation of which is explained with reference to FIG. 5.

FIG. 4 shows a schematic detailed view of the pressure limiting and holding valve 34 according to FIG. 2 in its first working position, in which it is closed. This first working position corresponds. (also) the rest position of the pressure limiting and holding valve 34, in which the first pressure p ₂ 8 in the first pressure chamber 28 corresponds to the second pressure p ₃ o in the second pressure chamber 30. In order for the working position shown in FIG. 4 to correspond to the rest position, it is necessary that the first spring 36, which is supported on the underside of the plate 42, generates a greater spring force than the second spring 56, which is located on the upper side 64 of the Plates 42 and the underside 62 of the valve plate 38 supports. Through such a design of the first spring 36 and the second spring 56, the valve plate 38 rests with its hemispherical surface 60 on the first valve seat 40, so that the pressure limiting and holding valve 34 is closed. Furthermore, the top 64 of the plate 42 bears against the stop 44. Although the first working position shown in FIG. 4 corresponds to the rest position of the pressure limiting and holding valve, this working position can also be assumed in other operating states, provided that the pressure difference between the first pressure p ₂ e and the second pressure p _{30 is} due to the spring constants of the first spring 36 and the second spring 56 does not exceed the specified value. For example, the first operating position may be men eingenom- to the second pressure p ₃ o to keep, when the first pressure p ₂₈ is smaller in the first pressure chamber 28 than the second pressure P ₃₀ in the second pressure chamber 30th FIG. 5 shows a schematic detailed view of the pressure limiting and holding valve 34 according to FIG. 2 in its second working position, in which it has an opening cross section. In this second working position of the valve disc 38 has moved to, for example, 50 to ^'downward, so that between the halbkugelförmigeή surface 60 of the valve disc 38 and the first valve seat an opening cross-section 40 is formed by the first under the pressure p ₂₈ standing fuel 10 from can flow to the first pressure chamber 28. The plate 42 lies in the second working position shown with its top 64 against the stop 44. However, since the plate 42 has a bore 52 and three grooves 54, a complete seal is not achieved by the surface 6 of the plate 42 resting against the stop 44. This is desirable so that the fuel 10 flowing between the valve plate 38 and the first valve seat 40 can flow into the second pressure chamber 30. It is possible to switch from the second working position of the pressure limiting and holding valve 34 shown in FIG. 5 either to the first working position explained with reference to FIG. 4 or to the third working position of the pressure limiting and holding valve explained below with reference to FIG. 6.

FIG. 6 shows a schematic detailed view of the pressure limiting and holding valve according to FIG. 2 in its unstable third working position. In this third working position, the valve plate 38 has moved downward, for example by 100 μm, with respect to the first working position, so that an opening cross section continues to exist between the hemispherical surface 60 of the valve plate 38 and the first valve seat 40. This opening cross section is preferably defined by the radius of the hemispherical surface 60 of the valve disk 38. The underside 62 of the valve plate 38 has exerted a force on the shaft 68, through which the plate 42, contrary to that through the first Spring 36 and the force caused by the second pressure p ₃ o, for example, has been moved down by 50 μm, so that the top 64 of the plate 42 no longer abuts the stop 44. 6, the first spring 36 is further pretensioned, so that the third pressure p ₃₂ required to open the nozzle needle 24 in the third pressure chamber 32 is increased.

FIG. 7 shows a schematic detailed view of the pressure limiting and holding valve 34 according to FIG. 2 in its fourth working position, in which it is also closed. This fourth working position corresponds to a pressure limiting position of the pressure limiting and holding valve 34. In this working position, the flat underside 62 of the

Valve plates 38 on the second valve seat 4.6, so that the pressure limiting and holding valve is closed. In order to achieve the fourth working position shown, the valve plate 38 has moved downward, for example by 150 μm, with respect to its rest position. It was on the

Creates 68 a force that moves the plate 42 downward, for example, 100 μm with respect to its rest position shown in FIGS. 4 and 5. As a result, the first spring 36 was further pretensioned in comparison to the third working position of the pressure limiting and holding valve 34 explained with reference to FIG. 6. The further prestressing of the first spring 36 further increases the third pressure p ₃₂ required to open the nozzle needle 26 in the third pressure chamber 32. The adjustment of the opening of the nozzle needle 26 required in the third pressure chamber 32 third pressure p ₃₂ can be used for example to provide different for a pilot injection and a main injection opening pressures.

FIG. 8 shows a curve which illustrates a possible course of the second pressure within the second pressure chamber as a function of the crankshaft angle, FIG. 9 shows FIG. 10 shows a curve which illustrates a possible course of the third pressure within the third pressure chamber as a function of the crankshaft angle and a curve which illustrates a possible injection course as a function of the crankshaft angle. The curves shown and other curves can be achieved in particular by a suitable control of the control valve 22. In Figures 8 to 10, the start of a pre-injection is marked with ° KW _V , while the start of the main injection is marked with ° KW _H. At the start of the pilot injection, the second pressure is p ₃ o in the second pressure chamber 30 is still relatively low, so that for opening the nozzle needle 26, a relatively low pilot injection opening pressure p ₃₂ v in the third pressure chamber 32 is sufficient, which is shown in Figure 9 , The pre-injection begins as soon as the pre-injection opening pressure p _{32v is reached} in the third pressure chamber 32, which can be seen from a comparison of _FIGS . 9 and 10. After the start of the pre-injection, the pressure limiting and holding valve -34 is in its second or third working position, so that the second pressure ρ ₃ o in the second pressure chamber 30 continues to increase, as shown in FIG. The third pressure p ₃₂ in the third pressure chamber 32 is also built up again after the pre-injection. Due to the now higher second pressure p ₃₀ in the second pressure chamber 30 and a first spring 36 which is further biased due to the position of the plate 42, the third pressure p ₃₂ H required in the third pressure chamber 32 to trigger the main injection is in comparison to that The pre-injection opening pressure p32v required for the pre-injection is significantly increased. As soon as this main injection opening pressure p ₃₂ H is reached in the third pressure chamber 32, the main injection begins, as can be seen from a comparison of FIGS. 9 and 10. Even after the start of the main injection, the second pressure p _{30 is} initially built up further in the second pressure chamber 30, as shown in FIG. 8. When the crankshaft position ° KW _A4 , the pressure limiting and holding valve 34 changes to its fourth working position. This will make the second pressure p ₃₀ limited in the second pressure chamber 30 and kept approximately constant over the remaining period of the main injection. After the main injection, the second pressure p ₃₀ decreases again in the second pressure chamber 30, for example due to the play between the nozzle needle piston 50 and the second pressure chamber 30. This is advantageous in order to achieve defined initial conditions for the next injection cycle. If the play between the nozzle needle piston 50 and the second pressure chamber 30 is not sufficiently large for a sufficiently rapid reduction of the second pressure p ₃ o, suitable bypasses can additionally or alternatively be provided. Of course, the curve profiles shown in FIGS. 8 to 10 vary, for example, as a function of the control of the control valve 22, the particular type of internal combustion engine, the load conditions, rotational speeds and so on.

The invention can be summarized as follows: The invention relates to a pump-nozzle unit for supplying fuel into a combustion chamber of an internal combustion engine. In order to enable a defined control of the injection process and the injection pressure in a compact design, a pressure limiting and holding valve is provided between a first pressure chamber, which can be filled with fuel under a first pressure by a fuel pump, and a second pressure chamber the second pressure chamber under a second pressure fuel exerts a closing force on the nozzle needle.

The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for realizing the invention both individually and in any combination.

Claims

claims

1. Pump-nozzle unit for supplying fuel (10) in a combustion chamber (12) of an internal combustion engine, with

a control and / or adjustable fuel pump (14-22),

a fuel injection nozzle (24) which has a nozzle needle 826) which can be moved back and forth between a closed position and an open position,

a first pressure chamber (28) which can be filled by the fuel pump (14-22) with fuel (10) under a first pressure (p ₂ s),

a second pressure chamber (30), fuel (10) in the second pressure chamber (30) under a second pressure (p ₃ o) exerting a closing force on the nozzle needle (26), and

a third pressure chamber (32) which communicates with the first pressure chamber (28), fuel (10) under a third pressure (p ₃ ) in the third pressure chamber (32) exerting an opening force on the nozzle needle (26),

that a pressure limiting and holding valve (34) is provided between the first pressure chamber (28) and the second pressure chamber (30).

2. Pump-nozzle unit according to claim 1, so that the pressure limiting and holding valve (34) is actuated by a pressure difference.

3. Pump-nozzle unit according to claim 2, characterized in that the pressure difference is the difference between the first pressure (p ₂ β) and the second pressure (p ₃ o).

4. Pump-nozzle unit according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the pressure limiting and holding valve (34) is a 2/3 valve.

5. Pump-nozzle unit according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the pressure limiting and holding valve has a first working position in which it is closed.

6. Pump-nozzle unit according to claim 5, so that the first working position is an idle position forced by spring forces.

7. Pump-nozzle unit according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the pressure limiting and holding valve (34) has a second working position with an opening cross section.

8. Pump-nozzle unit according to claim 7, so that the pressure limiting and holding valve (34) has an unstable third working position with an opening cross-section.

9. Pump-nozzle unit according to one of the preceding claims, characterized in that the pressure limiting and holding valve (34) has a fourth working position different from the first working position, in which it is closed.

10. Pump-nozzle unit according to claim 3 and 9, characterized in that the pressure limiting and holding valve (34) assumes the fourth working position when the first pressure (p ₂ s), the second pressure (p ₃₀ ) by a predetermined value exceeds.

11. Pump-nozzle unit according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that in the second pressure chamber (30) a first spring (36) is provided which exerts a closing force on the nozzle needle (26).

12. Pump-nozzle unit according to claim 11, so that the first spring (36) is biased differently depending on different working positions of the pressure limiting and holding valve (34).

13. Pump-nozzle unit according to one of the preceding claims, characterized in that the pressure limiting and holding valve (34) has a valve plate (38) which cooperates with a first valve seat (40) which is adjacent to the first pressure chamber (28) is provided.

14. Pump-nozzle unit according to one of the preceding claims, characterized in that the pressure limiting and holding valve ^■ (34) has a plate (42) which cooperates with a stop (44) which is adjacent to the second pressure chamber ( 30) is provided.

15. Pump-nozzle unit according to claim 13 and 14, characterized in that the valve plate (38) further with a second valve seat (46) cooperates, which is arranged between the first valve seat (40) and the stop (44).

16. Pump-nozzle unit according to claim 15 and 16, d a d u r c h g e k e n e z e i c h n e t that when the plate (42) against the stop (44) does not achieve a complete seal.

17. Pump-nozzle unit according to one of claims 5 to 16, characterized in that the ^' valve plate (38) bears in the first working position on the first valve seat (40).

18. ^• Pump-nozzle unit according to one of claims 7 to 17, characterized in that the valve disk (38) in the second working position does not rest on the first valve seat (40) and not on the second valve seat (46), and that Plate (42) abuts the stop (44) in the second working position.

19. Pump-nozzle unit according to one of claims 7 to 18, characterized in that the valve plate (38) in the third working position is not on the first valve seat (40) and not on the second valve seat ^' (46)', and that the plate (42) does not rest against the stop (44) in the third working position.

20. Pump-nozzle unit according to one of claims 9 to 19, characterized in that the valve plate (38) abuts the second valve seat (46) in the fourth working position, and that the plate (42) in the fourth working position is not on Stop (44) is present.

21. Pump-nozzle unit according to one of claims 9 to 20, characterized in that the first spring (36) is supported on the plate (42).

22. Pump-nozzle unit according to one of the preceding claims, that the fuel pump (14-22) has a fuel pump piston (14) driven by the internal combustion engine.

23. Pump-nozzle unit according to one of the preceding claims, characterized in that the fuel pump (14-22) has a control valve (22) with which the first pressure chamber (28) in whole or in part with respect to a low-pressure fuel region (18 ) is lockable.

24. Pump-nozzle unit according to claim 22, so that the control valve (22) is operated piezoelectrically.