EP1399666B1 - Fuel injection device - Google Patents

Description

State of the art

The invention relates to a fuel injection device according to the preamble of the independent claim. From DE 43 11 627 a fuel injection device is already known, in which an integrated pressure booster piston by means of a filling or emptying a rear space allows an increase in the fuel injection pressure beyond the value provided by a common rail system addition.

Advantages of the invention

The fuel injection device according to the invention with the characterizing features of independent claim 1 has the advantage that due to a drive exclusively via the rear space of the pressure booster, the drive losses in the high-pressure fuel system are smaller compared to a control via a temporarily connected to the high-pressure fuel source working space. In addition, the high-pressure region, in particular the high-pressure chamber, only relieved to rail pressure and not up to leak level, whereby the hydraulic efficiency is improved.

The measures listed in the dependent claims are advantageous developments and Improvements of the fuel injection device specified in the independent claim 1 possible.

A coaxial to the closing piston arrangement of the pressure booster advantageously allows a small-volume and cost-effective design.

If the function of the pressure chamber of the injector is taken over by the high pressure chamber of the pressure booster device, a reduced dead volume results after the pressure booster device, which still has to be compressed to high pressure. In addition, the amplitude of any vibrations occurring between the closing pressure chamber and the pressure chamber is reduced, since a shorter flow connection results. This results in a more reliable operation with the possibility of faster switching.

By using a fast-switching piezo valve as a control valve small injection quantities can be injected in a defined manner and with small quantity tolerances in the combustion chamber of an internal combustion engine even at high nozzle opening pressure; Moreover, due to the fast switching process, only small leakage losses result.

A variation of the switching speed, in particular in the case of a piezoelectric valve, which has a substantially linearly controllable piezoactuator, allows a change in the pressure rise gradient at the beginning of the injection, ie an injection rate shaping, and thus an optimum adaptation of the injection curve to the requirements of the engine.

If a 3/3-way piezo valve is used, then the intermediate position can be realized by partial stroke of the piezoelectric actuator and used to injection at low To generate pressure. Hereby, an injection course shaping, in particular a boat injection, is made possible and the metering of small amounts of fuel is improved.

By an optimized hydraulic adjustment, in particular a filling path of the high-pressure chamber, a further improved needle closing can be achieved. For this purpose, an acceleration phase is generated in which the pressure in the nozzle chamber is smaller than the pressure in the needle pressure chamber. This results in an additional hydraulic closing force on the nozzle needle and the acceleration phase when closing can be greatly reduced. Due to the faster needle closing, the volume characteristics become flatter in ballistic operation. By this additional hydraulic force a very stable needle closing and thus injection end is achieved. This increases the metering accuracy of the injector. Furthermore, a faster response of the nozzle needle is achieved at the control signal end, whereby a flatter mass flow characteristic is achieved in the ballistic range and the metering accuracy is further increased. At the same time an improvement of the exhaust emission values of the internal combustion engine can be expected by the faster needle closing.

Further advantages result from the further features mentioned in the further dependent claims and in the description.

drawing

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. FIG. 1 shows a fuel injection device, FIG. 2 shows a piezo valve, FIG. 3 shows a second fuel injection device, FIG. 4 another fuel injection device, Figure 5 shows two diagrams and Figure 6 three more diagrams. FIG. 7 shows a further alternative embodiment and FIG. 8 shows pressure curves associated with the arrangement according to FIG.

Description of the embodiments

In Figure 1, a fuel injection device is shown, in which a pressure booster 7 having fuel injector 1 is connected via a fuel line 4 with a high-pressure fuel source 2, wherein in line 4 on the side of the high-pressure fuel source, a throttle 3 and on the side of the injector with a second throttle 18 connected in parallel check valve 19 is arranged. The high-pressure fuel source includes a plurality of non-illustrated elements such as a fuel tank, a pump and the high-pressure rail of a conventional rail system known per se, wherein the pump provides up to 1600 bar high fuel pressure in the high-pressure rail by fuel from the tank in the High-pressure rail transported. In this case, for each cylinder of an internal combustion engine, a separate injector fed from the high-pressure rail is provided. The injector 1 shown by way of example in FIG. 1 has a fuel injection valve 6 with a closing piston 13, which protrudes with its injection openings 9 into the combustion chamber 5 of a cylinder of an internal combustion engine. The closing piston 13 is surrounded on a pressure shoulder 16 by a pressure chamber 17, which is connected via a high pressure line 40 to the high-pressure chamber 28 of the pressure booster device 7. The closing piston 13 protrudes at its end facing away from the combustion chamber, the guide region 14, into a closing pressure chamber 12 which, via a line 47, communicates with a space 26 connected to the high-pressure fuel source Pressure Translation device is connected. A rear space 27 of the pressure booster device can be connected via a fuel line 42, 45 and a 3/2-way valve 8 to the high-pressure fuel source 2. The valve 8 in this case connects the line 42 to the line 45 in a first position, while a low-pressure line 44 leading to a low-pressure system, not shown, is closed at its end connected to the valve 8. In a second position of the valve leading to the back space 27 line 42 is connected to the low pressure line 44, while the fuel high pressure source 2 facing away from and connected to the valve end of the line 45 is sealed. The closing piston is resiliently mounted via a return spring 11 arranged in the closing pressure chamber and tensioned between the housing 10 of the injection valve 6 and the closing piston 13, wherein the return spring presses the needle area 15 of the closing piston against the injection openings 9. The pressure booster 7 has a spring-mounted pressure booster piston 21, which separates the high-pressure line 40 connected to the high-pressure chamber 28 from the space 26 which is connected via the line 4 to the high-pressure fuel source 2. The spring 25 used for supporting the piston is arranged in the rear space 27 of the pressure booster device. The piston 21 is designed in two parts and has a first partial piston 22 and a smaller diameter second partial piston 23. The housing 20 of the pressure booster device is divided by the slidably disposed in the housing part piston 22 into two areas, which are liquid-tight separated from each other except for leakage losses. The one area is the space 26 connected to the high pressure source, the second area has a step-like taper. It contains the second sub-piston 23, which dips into the taper and liquid-tight from the rest of the second Area delimiting, which forms the back space 27. The region of the tapered portion delimited by the partial piston 23 forms the high-pressure space 28 of the pressure booster device which is connected to the pressure chamber 17 of the injection valve and which is connected via a check valve 29 and a fuel line 49 to the line 47 or the closing pressure chamber 12. The two sub-pistons are separate components, but can also be designed to be firmly connected to each other. The second part piston 23 has at its end facing the first part of the piston a projecting beyond its diameter spring holder 24, so that the tensioned against the housing 20 return spring 25 presses the second part of the piston against the first.

The pressure of the high-pressure fuel source 2 is fed via the line 4 to the injector. In the first position of the valve 8, the injection valve is not activated and there is no injection. Then, the rail pressure is in the space 26, the valve 8, via the valve 8 and the line 42 in the back space 27, in the closing pressure chamber 12 and via the check valve 29 containing line 49 in the high-pressure chamber 28 and in the pressure chamber 17 at. Thus, all pressure chambers of the pressure booster device are subjected to rail pressure and the pressure booster piston is pressure-balanced, that is, the pressure booster device is deactivated and there is no pressure gain instead. The pressure booster piston is returned to its original position in this state via a return spring. The high pressure chamber 28 is filled via the check valve 29 with fuel. Due to the rail pressure in the closing pressure chamber 12, a hydraulic closing force is applied to the closing piston. In addition, the return spring 11 provides a closing spring force. Therefore, the rail pressure can constantly pending in the pressure chamber 17 without the injector opens unintentionally. Only when the pressure in the nozzle chamber rises above the rail pressure, which is achieved by switching on of the pressure booster is reached, opens the nozzle needle and the injection begins. The metering of the fuel into the combustion chamber 5 is effected by activation of the 3/2-way valve 8, that is by transferring the valve to its second position. As a result, the rear space 27 is separated from the high-pressure fuel source and connected to the return line 44, and the pressure in the rear space drops. This activates the pressure booster device, the two-part piston compresses the fuel in the high-pressure chamber 28, so that in the pressure chamber 17 connected to the high-pressure chamber, the pressure force acting in the opening direction increases and the closing piston releases the injection openings. As long as the rear space 27 is pressure-relieved, the pressure booster device remains activated and compresses the fuel in the high-pressure space 28. The compressed fuel is forwarded to the injection openings and injected into the combustion chamber. To end the injection, the valve 8 is returned to its first position. This separates the rear space 27 from the return line 44 and connects it again to the supply pressure of the high-pressure fuel source or the high-pressure rail of the common rail system. As a result, the pressure in the high-pressure chamber drops to rail pressure, and since rail pressure is again present in the pressure chamber 17, the closing piston is hydraulically balanced and is closed by the force of the spring 11, whereby the injection process is completed. After pressure equalization of the system, the pressure booster piston is returned by a return spring to its original position, the high-pressure chamber 28 is filled via the check valve 29 and the line 49 from the high-pressure fuel source. The throttle 3 and the check valve 19 with the parallel-connected throttle 18 serve to dampen vibrations between the high-pressure fuel source and the injector, which otherwise the needle closing, in particular possibly to be performed multiple injections, that is short consecutive closing and opening operations would affect.

In an alternative embodiment, the check valve 29 may also be integrated in the pressure booster piston. In both the alternative integrated and in the pictured separate embodiment, the check valve 29 may be connected to the rear space 27 instead of the closing pressure chamber 12, so that the filling of the high-pressure chamber takes place from the back space 27 instead of from the closing pressure chamber 12 when the injection valve is closed. The anti-vibration throttles 3 and 45 (the latter with the check valve connected in parallel) may be mounted anywhere between the high-pressure fuel source and the space 26 of the injector. It is also possible to use other pressure intensification devices which can be controlled via a back space, for example those having a two-part pressure booster piston, in which the check valve required for filling the high-pressure space is integrated in the second (diameter-thin) partial piston.

The 3/2-way valve 8 contained in the arrangements of Figure 1 and 3 can be designed both as a magnetically and as a piezoelectrically controllable valve according to Figure 2. In the piezoelectric embodiment as a 3/2 valve according to FIG. 2, a valve housing 50 is connected to the three connection lines 42, 44 and 45 known from FIG. In the valve housing is a movably mounted valve body 51, which is pressed in the rest position shown by a return spring 52, which is stretched between it and the valve housing, with its hemispherical side surface liquid-sealing against the first valve seat 53. The opposite side of the valve body, which is formed by a flat surface, is the one with the line 45th connected second valve seat 54 opposite. In the rest position shown, a gap between the valve body and the second valve seat is present. From the first valve seat 53, a pipe 55 leads, at the end remote from the valve body, the low-pressure line 44 is connected. A first power transmission piston 56 rests on the tube sealing the hemispherical side surface of the valve body and protrudes through a sealed opening of the side facing away from the valve body of the pipe out of the pipe so that a force is exerted on the valve body from outside the valve housing by displacement of the power transmission piston can. A widened end piece of the piston 56 projects into a schematically illustrated coupling space 58 filled with coupler liquid, for example fuel. This fuel used as a coupler liquid comes for example from a low-pressure system, from where it is supplied via a line not shown. On the opposite side of the coupling space, a second power transmission piston 57 protrudes into the coupling space. The latter is attached to an electrically controllable piezoelectric actuator 59, which may vary in length by applying an electrical voltage, wherein a fixed to the opposite side of the piezoelectric actuator bottom element 60 has the same distance in each electrical state of the piezoelectric actuator to the coupling space.

The illustrated position of the valve body forms the first position of the 3/2-way valve. In this state, the valve body closes the connection of the tube with the space in which the valve body is movably mounted, so that the line 42 can exchange fuel exclusively with the line 45. If the valve is to be transferred to its second position in order to achieve a metering of fuel into the combustion chamber, the piezoactuator 59 must be electrically actuated. To compensate for Temperature-dependent changes in length of the piezoelectric actuator and with a suitable design of the coupling space 58 is also shown schematically for force / displacement translation of the piezoelectric actuator with the power transmission piston 56 via the power transmission piston 57 and the coupling space 58 in contact. If the piezoelectric actuator is driven, it expands, and it is transmitted through the coupling space through a force on the valve body, which lifts it from the first valve seat and presses against the second valve seat, so now not the line 45, but the line 44 with the line 42 is connected.

The piezo valve can, as shown in FIGS. 1 and 3, be connected to the line 4 by means of the line 45. Alternatively, the valve may be connected directly to the space 26 instead of the line 4. The valve body can also have other shapes, which means that piezoelectrically actuable slide valves, flat seat valves or conical seat valves or any combination can also be used. If intermediate positions are provided between the first and the second position in order to relieve the backspace only slowly and to build up the fuel pressure in the high-pressure space correspondingly slowly, it may be advantageous to use a valve as a switching valve which has no opening overlap of the two valve seats, that is to say in that, for example, the second valve seat is first closed before the first valve seat slowly opens. As a result, a loss amount of fuel is avoided with slow valve switching in the transition region, since at no time there is a connection from the rail to the return system. For this purpose, a seat slide valve can be used. The piezo valve can also be designed as a 3/3-way valve by at least one middle position of the valve body via a corresponding electrical control of the piezoelectric actuator as an alternative to or in combination with a slow drive is provided, which persists for a certain time, so that, for example, pre-injections can be realized at constant low pressure levels. In this case, however, a connection of the line 42 to both the line 45 and the line 44 must exist in the at least one middle position, so that a constant pressure intermediate level can form in the rear space and thus also in the high-pressure space. The pressure intermediate level in the rear space is defined by the flow cross sections of the valve seats 53 and 54. In this case, it is advantageous to make the cross-sectional areas of the valve seats larger than the cross-sectional areas of the feed line 45 or of the tube 55 and to choose such that the intermediate pressure level is determined only by the corresponding inflow and outflow cross sections of the feed lines 42, 44 and 45. This results in the middle position, a stroke range of the valve body, which has no effect on the value of the intermediate pressure level. Thus, any stroke tolerances of the piezo actuator remain without influence on the injection process.

FIG. 3 illustrates a further embodiment with a pressure booster device integrated in the injector housing 100. The same components as shown in Figure 1 are provided with the same reference numerals and will not be described again. In the injector three relatively movable parts are resiliently mounted: a pressure booster piston 121, a closing piston 113 and a valve piston 206. The pressure booster piston 121 has a first partial piston 122 and a second partial piston 123. The first sub-piston 122 is guided in a liquid-tight manner from the injector housing, except for leakage losses. On the one hand, the first part piston has a step-shaped taper, so that the return spring 125 of the pressure booster device space between the injector and the first part of the piston place. The restoring spring 125 is stretched between a spring holder 124 arranged on the taper and a limiting element 200 fastened to the injector housing, the side of the limiting element facing away from the restoring element serving as a stop for the pressure booster piston in order to prevent abutment of the taper of the first partial piston on the injector housing. The space 126 between the first sub-piston and the injector, in which the return spring 125 is located, corresponds to the space 26 of Figure 1 and is like this connected via the line 4 to the high-pressure fuel source 2. The first partial piston 122 moves on the side facing away from the space 126 in the smaller-diameter second partial piston 123, which is partially also performed by the injector, since this has a step-shaped taper in the region of the second part piston. The space between the second sub-piston and the injector housing forms the rear space 127 of the pressure booster. The pressure booster piston is designed as a hollow piston: a central continuous bore 130 in the pressure booster piston connects the chamber 126 hydraulically with the end of the closing piston 113, which projects into the space 126 remote from the end of the bore, which thus serves as a closing pressure chamber 112. The opposite end of the closing piston, the needle portion 115, closes the injection openings 9. Between the protruding into the closing pressure chamber region of the closing piston and the needle area is the guide portion 114 of the closing piston, which ensures axial guidance of the closing piston along the injector, which in the Closing piston according to a second step-shaped taper. The guide area is preferably larger in diameter than the needle area. The guide region is traversed by a flow connection 205, for example in the form of a continuous bore, so that the gap between the needle region and the Injector and the adjoining beyond the needle portion of the guide portion gap between a smaller diameter portion of the closing piston and the housing can exchange fuel with each other. A return spring 131 presses the closing piston against the injection openings. The valve hollow piston has an end tapering towards a circular sealing edge, which is pressed against the end face of the second partial piston by the return spring 111, so that the high-pressure chamber 128 which is formed by the space lying between the closing piston and the injector housing, beyond the valve hollow piston, can be sealed against the closing pressure chamber 112, that is, the valve hollow piston together with the end face of the second part piston can serve as a check valve 129. Between the projecting into the bore 130 portion and the injection openings facing the end of the needle portion of the closing piston has two areas with a diameter which is smaller than the diameter in the projecting into the closing pressure area: on the one hand a waist between the guide area and in the Hole projecting area, on the other hand, the area between the guide portion and the injection openings facing the end of the closing piston. At the injector housing 100 in the region of the space 126 a in the form of a cylinder projecting into the bore 130 spacer 132 is attached. On the side facing the closing piston, the spacer 132 has a taper, on which a closing space spring 131 is wound, which presses against the projecting into the bore 130 end of the closing piston, wherein between the closing piston and the spacer is sufficient clearance to a lifting the closing piston of the injection openings to initiate an injection process. With suitable dimensioning, the spacer limits the stroke of the closing piston to the extent required for an injection process.

In the arrangement according to FIG. 3, the high-pressure chamber 28 and the nozzle chamber 17 of the arrangement according to FIG. 1 coincide and are formed by the high-pressure chamber 128. The operation is otherwise similar to that of the arrangement of Figure 1. The check valve for filling the high-pressure chamber 128 is formed by the check valve 129 described above. The metering of the fuel into the combustion chamber 5 is also carried out by activation of the 3/2-way control valve 8. As a result, the back space 127 is depressurized and the pressure booster activated. The fuel in the high-pressure chamber 128 is compressed and forwarded via the connection 205 to the injector tip. The closing piston finally releases the injection openings as a result of the increasing opening pressure force in the high-pressure chamber, and the fuel is injected into the combustion chamber. The injection pressure is thus higher than the rail pressure from the beginning. The valve hollow piston 206 in this case seals the high-pressure chamber 128 with a guide relative to the closing piston, the valve hollow piston being axially displaceable and moving toward the injection openings together with the pressure booster piston during the compression of the fuel in the high-pressure chamber. Likewise, as already stated, the hollow valve piston seals the high-pressure chamber with its sealing seat relative to the second partial piston. This ensures that no compressed fuel can flow back into the closing pressure chamber. To end the injection is separated by the control valve 8, the rear space 127 of the conduit 44 and connected to the high-pressure fuel source 2, which builds up in the back space of the rail pressure and the pressure in the high pressure chamber drops to rail pressure. The closing piston is now hydraulically balanced and is closed by the force of the closing space spring 131, which ends the injection process. As a result of the pressure equalization now also the pressure booster piston 121 is returned by the return spring 125 in its initial position, wherein the high pressure chamber 128 is filled via the check valve 129 from the closing pressure chamber 112, which in turn is fed from the space 126 with fuel.

To stabilize the switching sequences additional structural measures for damping possibly occurring between the high-pressure fuel source and the injector vibrations can be made. In addition to a suitable design of the throttle 3 and alternatively or in combination throttle check valves at any point of the leads 4, 42 and 45 can be installed. In addition, the pressure booster piston, the closing piston and the valve hollow piston may also have different shapes. It is essential in the case of a closing piston that, on the one hand, a fuel supply is ensured up to the injection openings and that in the area of the high-pressure space the fuel pressure encounters an attack surface which effectively leads to an axial force on the closing piston, which is oriented towards the pressure booster piston, that is to say in FIG Opening direction acts.

Figure 4 illustrates another design of an injector with integrated pressure booster device. In contrast to the arrangement according to FIG. 3, the closing piston 113 is guided in a liquid-tight manner by the guide region 210 of the second partial piston 123, except for leakage losses. The valve hollow piston 206 from FIG. 3 can therefore be dispensed with, for which purpose a separate non-return valve 215 must be provided for filling the high-pressure space 128, which in the example shown is connected to the rear space 127. As in the arrangement of Figure 1 or 3, the space 126 and the closing pressure chamber 112 constantly exchange fuel with each other, wherein in contrast to the arrangement of Figure 3, the pressure translator piston resetting spring 217 is not located in the space 126, but in the rear space 127 where between a stepped narrowing of the Injector housing and the first sub-piston 122 is stretched. A limiting element 218 fastened to the injector housing limits the freedom of movement of the pressure booster piston so that the space 126 always has a volume different from zero.

In alternative embodiments, the check valve 215 may be connected to the space 126 or directly to the conduit 4 instead of the back space 127. The check valve may also be integrated in the pressure booster piston 121 or in the closing piston 113.

In all embodiments, the closing pressure chamber 12 or 112 and the space 26 or 126 are realized by a common closing pressure working space (12, 26, 47) or (112, 126, 130), wherein all partial areas (12, 26) or (112, 126) of the closing pressure working chamber are permanently connected to one another for the purpose of exchanging fuel, for example via at least one fuel line 47 or via at least one bore 130 integrated in the pressure booster piston. The pressure chamber 17 and the high-pressure chamber 28 can also be replaced by a common injection space (17, FIG. 28, 40) are formed, wherein all portions of the injection space are permanently connected to each other for the exchange of fuel. The pressure chamber 17 and the high-pressure chamber 28 can in this case be connected to one another via a fuel line 40 (cf. FIG. 1), or the pressure chamber can be formed by the high-pressure chamber (128) itself (compare FIGS. 3 and 4).

FIG. 5 shows the time profiles of the fuel pressure p in the high-pressure chamber 28 or 128. The curve 310 represents the pressure conditions for rapid actuation of the 3/2 piezo valve according to FIG. 2, the curve 311 for slow valve actuation. The first position of the valve, in which the valve body is pressed against the first valve seat 53, is hereinafter referred to as the rest position and the second position, in which the valve body is pressed against the second valve seat 54, as the end position designated. With rapid valve actuation of the piezoelectric actuator is electrically driven so that the valve body quickly passes from the rest position to the end position, with slow valve actuation applied to the piezoelectric actuator voltage is slowly increased, so that the valve body passes with low speed from the rest position to the end position. The curves 320 and 321 show the associated pressure curves in the rear space of the pressure booster as a function of the time t. The resulting stroke h of the piezoactuator, ie the movement of the valve body, is shown in curves 330 and 331. Prail designates the pressure of the high-pressure fuel source or the pressure in the high-pressure rail of the common-rail system, pmax the maximum achievable in the high-pressure chamber fuel pressure and hmax the maximum stroke of the valve body.

In the rest position of the valve body of the pressure booster is deactivated and reset the piston of the pressure booster in its initial position, there is no injection. In both the high pressure space and the rear space, rail pressure prevails (see curves 310, 311, 320 and 321 in the period from zero to time t1). In the end position hmax of the valve body, the pressure booster is fully activated, the pressure in the backspace drops to a small value close to zero and the pressure in the high-pressure chamber reaches its maximum value pmax. The closing piston is lifted and an injection takes place. In a transition region between the rest position and the end position of the pressure intensifier is here partially activated, the pressure in the rear space decreases with increasing stroke of the piezo valve and the pressure booster piston generates a mean injection pressure, which increases with increasing valve lift, so that the injection proceeds with increasing pressure. In the diagrams shown in FIG. 5, for the purpose of a simplified illustration, it is assumed that the nozzle opening pressure differs only insignificantly from the rail pressure. When the valve is actuated slowly from time t1 (curve 331), the pressure in the backspace continuously drops to a low value until time t2 (curve 321), while the pressure in the high-pressure chamber slowly increases to the value pmax (curve 311). When the nozzle opening pressure reaches shortly after t1, the closing piston rises from the injection ports and opens completely, so that an increasing amount of fuel is injected with increasing pressure. At time t2, the maximum opening stroke hmax of the valve body and the maximum injection pressure pmax are reached. The closing operation at time t3 occurs quickly to ensure a rapid pressure reduction at the end of injection (the term "rapid spill" is used for this purpose in English). So at time t3, in which the extension of the piezoelectric actuator is reversed, the pressure is returned both in the high-pressure chamber and in the rear space to the rail pressure level and the closing piston closes the injection openings again. If, on the other hand, the valve is actuated rapidly at the time t1 (curve 330), the transition region is traversed rapidly and the pressure in the high-pressure chamber rises considerably up to the maximum level pmax before the time t2 (see curve 310), while at the same time the pressure in the rear chamber rapidly increases low value (see curve 320). Accordingly, there is a quasi-rectangular pressure curve 310. The closing operation is preferably carried out in an analogous manner to the case described above, quickly, in order to ensure a rapid pressure reduction at the end of injection.

FIG. 6 shows the pressure conditions for the case in which, for example, the piezo valve according to FIG. 2 is operated as a 3/3-way valve. In addition to the rest position and the end position of the valve body of the valve in this case also has a central position in which it can remain for at least a certain period of time and in which the line 42 is connected to both the conduit 45 and the conduit 44. Then, in this period, a pressure equilibrium at an intermediate pressure level PZ1 can set in the rear space, which is determined together by the amount flowing into the low-pressure system and that flowing from the high-pressure fuel source. The curve 410 shows the pressure curve in the high-pressure chamber, the curve 420 shows the pressure curve in the rear chamber. The h (t) diagram underneath shows the time curve of the stroke of the closing piston, the third diagram shows the time curve of the piezo stroke H, ie the movement of the valve body.

Hmax denotes the maximum value for the piezohub, with which the end position of the valve body can be adjusted, in which the back space is only connected to the low-pressure system. The opening pressure pö in the high-pressure chamber is the pressure required to raise the closing piston. t1 to t5 designate various successive times within one injection cycle, which includes a boot injection, that is, a first injection phase at a low pressure level, and a second injection phase at a high pressure level.

At the time t1, the valve body is transferred by a corresponding control of the piezoelectric actuator in the middle position and held until the time t3 in this middle position (see the H (t) diagram). In the rear space, the pressure drops to the intermediate pressure level PZ1, while the pressure in the high-pressure chamber rises slowly. As soon as it exceeds the opening pressure at time t2, the injector opens (see the h (t) diagram) and there is a boat injection phase at a pressure level between the rail pressure level and the maximum achievable with the pressure intensifier pressure value. At time t3, the piezo valve is transferred to its end position (second position) with the stroke value Hmax, so that the pressure in the back space drops to a low value near zero, while the injection openings remain open and the pressure in the high-pressure chamber increases to the value pmax. This main injection phase lasts until time t4, in which the valve is returned to its rest position (H = 0), so that pressure equalization takes place at the rail pressure level in the high-pressure chamber and in the rear space and a short time later at time t5 the closing piston closes the injection openings (h = 0).

Alternatively, the intermediate position can also be used for injection with a low injection pressure, with the intermediate position returning to the rest position. This happens, for example, with small injection quantities, as required in a pilot injection or idle.

In all embodiments, the closing pressure chamber 12 and 112 and the space 26 or 126 by a common working space (12, 47, 26) or (112, 130, 126) realized, wherein all portions of the working space are permanently connected to each other for the exchange of fuel, for example via at least one fuel line 47 or at least one integrated in the pressure booster piston bore 130. The pressure chamber 17 and the high pressure chamber 28 may also be formed by a common injection space (17, 28, 40), wherein all portions of the injection space are permanently connected to each other for the exchange of fuel. The pressure chamber 17 and the high-pressure chamber 28 can in this case be connected to one another via a fuel line 40 (cf. FIG. 1), or the pressure chamber can be formed by the high-pressure chamber (128) itself (compare FIGS. 3 and 4).

FIG. 7 shows a modification of the embodiment according to FIG. 1, in which, with an otherwise identical construction, a throttle 520 is additionally installed in the line 49, so that the connection between the high-pressure chamber 28 and the closing pressure chamber 12 or the space 26 is throttled. The cross section of the connection path of the 3/2-way valve 8 between the line 45 and the line 42 is provided with the reference numeral 510 and is referred to below as the valve cross-section.

By a suitable adjustment of the valve cross section 510, which connects the rear space 27 with the pressure supply, and the flow cross section of the filling path 49 by a suitable choice of the flow cross section of the throttle 520, an additional hydraulic force for needle closing can be generated. For this purpose, the filling path 49 is designed very small by the throttle 520, but large enough to allow filling of the high-pressure chamber 28 and a reset of the pressure booster piston until the next injection. Further, the valve cross-section 510 is designed large enough so that in the back space 27, a rapid pressure build-up takes place at rail pressure, depending on the line design and a pressure increase in the back space can take place. Due to the rapid pressure build-up in the rear space, a rapid pressure reduction takes place in the high-pressure chamber 28 Rail pressure with subsequent pressure undershoot under rail pressure instead. By the throttle 520 too fast pressure equalization between space 28 and space 12 and 26 is prevented. Since rail pressure continues to be present in the closing pressure chamber 12 in this phase, a closing hydraulic force acts on the nozzle needle.

In a further alternative embodiment, the design of the flow cross-section of the filling path 49 is ensured by a non-return valve 29 having a corresponding flow cross-section instead of the use of a throttle.

Figure 8 shows schematically the achievable with the arrangement of Figure 7 pressure gradients. Here, the time profile of the fuel pressure in the high pressure chamber 28 is provided with the reference numeral 1310, the time course of the fuel pressure in the rear space 27 of the pressure booster with the reference numeral 1320th

In this case, the injection end is as follows: After deactivating the valve 8 takes place in the back space 27 and the closing pressure chamber 12, a pressure build-up to rail pressure, which simultaneously takes place in the high-pressure chamber 28 and the pressure chamber 17, a rapid pressure drop to rail pressure. The last-mentioned pressure drop occurs so fast that an undershoot of the pressure in the high-pressure chamber and in the pressure chamber takes place under the rail pressure. It is at this stage that the needle closing takes place, so that an additional hydraulic pressure force on the nozzle needle occurs, whereby a fast needle closing can be achieved and the amounts of fuel can be metered even more accurately into the combustion chambers of the internal combustion engine. In the further course, the rail pressure also sets in the high-pressure chamber and in the pressure chamber. The overshoot over the rail pressure, drawn in the course 1320, is hydraulically conditioned and can be minimized or suppressed by suitable line design. Essential for the rapid pressure drop with the following undershoot under rail pressure in the high pressure chamber is the rapid pressure build-up in the back room.

Claims (16)

1. Fuel injection device for internal combustion engines having a fuel injector (1) which can be fed by a high-pressure fuel source (2), a pressure booster device (7), which has a moveable pressure booster piston (21; 121), being connected between the fuel injector (1) and the high-pressure fuel source (2), the pressure booster piston (21; 121) separating a space (26; 126) which can be connected to the high-pressure fuel source (2) from a high-pressure space (28; 128) which is connected to the fuel injector, it being possible for the fuel pressure in the high-pressure space (28; 128) to be varied by filling a rear space (27; 127) of the pressure booster device (7) with fuel or emptying fuel out of the rear space (27; 127), the fuel injector (1) having a moveable closing piston (13; 113) for opening and closing injection openings (9), the closing piston (13; 113) projecting into a closing pressure space (12; 112), so that fuel pressure can be applied to the closing piston in order to exert a force on the closing piston in the closing direction, characterized in that the closing pressure space (12; 112) and the space (26; 126) are formed by a common working space, all the partial regions (12, 47, 26; 112, 130, 126) of the working space being permanently connected to one another for the exchange of fuel.
2. Fuel injection device according to Claim 1, characterized in that the pressure booster piston (121) is arranged coaxially with respect to the closing piston (113), and in that that partial region (112) of the working space which adjoins the closing piston (113) is connected to the other partial regions of the working space by means of a bore (130) which is integrated into the pressure booster piston (121).
3. Fuel injection device according to Claim 2, characterized in that that end of the closing piston (113) which is remote from the injection openings (9) is guided through the bore (130) such that it is liquid-tight except for leakage losses.
4. Fuel injection device according to one of the preceding claims, characterized in that the fuel injector has a pressure space (17; 205, 128) for supplying the injection openings (9) with fuel and for exerting a force on the closing piston (13; 113) in the opening direction.
5. Fuel injection device according to Claim 4, characterized in that the pressure space (17; 205, 128) and the high-pressure space (28; 128) are formed by a common injection space (17, 28, 40; 205, 128), all the partial regions (17, 28; 205, 128) of the injection space being permanently connected to one another for the exchange of fuel.
6. Fuel injection device according to Claim 5, characterized in that the pressure space (17) and the high-pressure space (28) are connected to one another by means of a fuel line (40).
7. Fuel injection device according to Claim 5, characterized in that the pressure space is formed by the high-pressure space (128).
8. Fuel injection device according to one of the preceding claims, characterized in that the closing pressure space (112) and the rear space (127) are delimited from one another by means of a piston part (123) of the pressure booster piston (121).
9. Fuel injection device according to one of the preceding claims, characterized in that the high-pressure space (28; 128) is connected to the closing pressure space (12; 112) by means of a non-return valve (29; 129).
10. Fuel injection device according to Claim 9, characterized in that the connection between the high-pressure space and the closing pressure space is throttled (520; 29) in such a way that, during a closing process, it is possible for the pressure in the pressure space to oscillate to values below the pressure of the high-pressure fuel source.
11. Fuel injection device according to one of Claims 1 to 8, characterized in that the high-pressure space (128) is connected to the rear space (127) by means of a non-return valve (215).
12. Fuel injection device according to one of the preceding claims, characterized in that the rear space (27; 127) can be selectively connected, by means of a valve (8), to a low-pressure line (44) or to the high-pressure fuel source (2).
13. Fuel injection device according to Claim 12, characterized in that the valve (8) is a piezoelectric valve having a first position and a second position, the piezoelectric valve connecting the rear space to the high-pressure fuel source (2) in a first position and to the low-pressure line (44) in a second position.
14. Fuel injection device according to Claim 13, characterized in that the piezoelectric valve is embodied in such a way that the speed of the transition between the first position and the second position can be varied.
15. Fuel injection device according to one of Claims 12 to 14, characterized in that the valve (8) can be moved into at least one intermediate position, so that an intermediate pressure level is produced in the rear space (27; 127).
16. Fuel injection device according to Claim 15, characterized in that in the intermediate position, the valve connects the rear space both to the high-pressure fuel source (2) and to the low-pressure line (44).

Images