WO2002093001A1

WO2002093001A1 - Fuel injection device

Info

Publication number: WO2002093001A1
Application number: PCT/DE2002/001550
Authority: WO
Inventors: Christoph Magel
Original assignee: Robert Bosch Gmbh
Priority date: 2001-05-17
Filing date: 2002-04-27
Publication date: 2002-11-21
Also published as: JP4129186B2; EP1392967A1; EP1392967B1; JP2004519614A; KR20030017632A; DE50209869D1; KR100853894B1

Abstract

A fuel injection device for internal combustion engines with a fuel injector supplied by a high pressure fuel source and a pressure amplification device is disclosed. The closing piston (13, 113) of the injector extends into a closing pressure chamber (12, 112), such that the closing piston may be pressurised by fuel pressure to produce a force, acting on the closing piston in the closing direction. The closing pressure chamber (12, 112) and the return chamber (27, 127) of the pressure amplification device are formed by a common closing pressure/return chamber (12, 27, 41, 112, 127, 141). All the partial regions (12, 27, 112, 127) of the closing pressure/return chamber are permanently connected to each other (41, 141) for the exchange of fuel, so that despite a low pressure amplification by the pressure amplification device, a relatively low injection opening pressure may be achieved.

Description

Kraftstoffeinspritzeinrichtunα

State of the art

The invention is based on one

Fuel injection device according to the preamble of the independent claim. From DE 43 11 627 fuel injection devices are already known in which an integrated pressure booster piston by means of a filling or an emptying of a rear space

Enables the fuel injection pressure to be increased beyond the value provided by a common rail system.

An injection system is known from US Pat. No. 6,113,000 which has a high-pressure reservoir and a medium-pressure reservoir, the high-pressure reservoir optionally also being able to be run with fuel.

DE 199 10 970 describes fuel injection devices with a pressure booster, the injector and the pressure booster each being assigned a separate control valve.

DE 43 11 627 also describes an injection device which, in addition to a control valve, requires an additional four-way slide valve.

Advantages of the invention

In contrast, the fuel injection device according to the invention with the characterizing features of the independent claim has the advantage of being a pressure-controlled device with the use of pressure booster devices to realize a small pressure amplification ratio, for example in the order of magnitude 1: 1.5 to 1: 3, relatively low injection opening pressures. A small pressure transmission ratio is advantageous because it allows the space available for the injector or the pressure intensifier to be kept small, the small volumes result in high dynamics in pressure build-up and reduction, relaxation losses are reduced to a minimum, the volume flows in the system and the delivery rate Fuel pump remain low and the necessary pressure level in the pump and rail remains in the range of up to 1400 bar, which is already manageable in series production, even at high injection pressures of over 2000 bar. The volume flows in the low pressure system also remain low. The arrangement according to the invention enables these advantages to be used even for applications in which small amounts of fuel have to be measured reliably. This is achieved by relieving the pressure in the closing pressure chamber at the moment when the fuel is to be injected. So that a little

Gear ratio can be realized without the opening pressure taking on too high values that would make an exact metering of small amounts of fuel impossible. In addition, a high closing pressure is still guaranteed, which leads to rapid needle closing under high injection pressure. It is particularly advantageous that at least the fuel pressure of the high-pressure fuel source can be constantly present in the high-pressure chamber (apart from pressure vibrations occurring in the system). This advantageously ensures that a high injection pressure is present at the injection openings as soon as the injector is opened and that fuel can be metered into the combustion chambers in a precisely metered manner within small time windows. In addition, the construction of the pressure intensifier can be simple and robust, since in addition to the low-pressure system, only another fuel system with a higher fuel pressure is provided. The measures listed in the dependent claims allow advantageous developments and improvements of the fuel injection device specified in the independent claim.

If the function of the pressure chamber of the injector is taken over by the high pressure chamber of the pressure booster, there is a reduced dead volume behind the pressure booster, which still has to be compressed to high pressure. In addition, the amplitude of any vibrations that occur between the closing pressure chamber and the pressure chamber is reduced, since there is a shorter flow connection from the closing pressure chamber to the pressure chamber. Overall, this results in a more reliable mode of operation with the possibility of faster switching.

In a further advantageous embodiment, with a diametrical arrangement of the line openings into the spaces of the pressure booster device and / or the closing pressure space, it can be achieved that the rooms are continuously flowed through during operation. Especially with small injection quantities, this also ensures that the rooms are continuously flowed through. As a result, local overheating of the fuel in the rooms as a result of constant compression and relaxation and thus also component damage can be avoided. It also prevents dirt from accumulating in the rooms.

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

drawing Embodiments of the invention are shown in the drawing and explained in more detail in the following description. 1 shows a

Fuel injection device, FIG. 2 shows two diagrams, FIG. 3 shows a second fuel injection device, FIG. 4 shows a piezo valve and FIG. 5 shows another one

Fuel injector. Figure 6 shows diagrams with pressure ratios for different switching speeds and Figure 7 illustrates the switching states when using a 3/3 valve. Figure 8 shows another

Fuel injection device, FIG. 9 further diagrams and FIG. 10 a further alternative embodiment.

Description of the embodiments

FIG. 1 shows a fuel injection device in which a fuel injector 1 having a pressure booster device 7 is connected to a high-pressure fuel source 2 via a fuel line 4 provided with a throttle 3. The high-pressure fuel source comprises a number of elements, not shown, such as a fuel tank, a pump and the high-pressure rail of a common rail system known per se, the pump being up to 1600 bar high

Provides fuel pressure in the high pressure rail by delivering fuel from the tank to the high pressure rail. A separate injector fed from the high pressure rail is provided for each cylinder of an internal combustion engine. The example shown in Figure 1

Injector 1 has a fuel injection valve 6 with a closing piston 13, which projects 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 to the high pressure chamber 28 of the pressure transmission device 7 via a high pressure line 40. The At its end facing away from the combustion chamber, the guide area 14, the closing piston 13 projects into a closing pressure chamber 12, which is connected via a line 41 to a rear chamber 27 of the pressure booster device and via a fuel line 42, 45 connected to the rear chamber 27 and a 3/2 way - Valve 8 can be connected to the high-pressure fuel source 2. In a first position, valve 8 connects line 42 to line 45, while a low-pressure line 44 leading to a low-pressure system, not shown, is closed at its end connected to valve 8. In a second position of the valve, the line 42 leading to the rear space 27 or to the closing pressure space 12 is connected to the low pressure line 44, while the end of the line 45 facing away from the high-pressure fuel source 2 and connected to the valve is sealed. The

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, the return spring pressing the needle region 15 of the closing piston against the injection openings 9. The pressure booster 7 has a spring-loaded pressure booster piston 21, which separates the high-pressure chamber 28 connected to the high-pressure line 40 from a chamber 26 which is connected to the high-pressure fuel source 2 via the line 4. The for

Storage of the piston used spring 25 is arranged in the rear space 27 of the pressure booster. The piston 21 is made in two parts and has a first partial piston 22 and a smaller-diameter second partial piston 23. The housing 20 of the

The pressure booster device is divided into two areas by the partial piston 22, which is displaceably arranged in the housing and is separated from one another in a liquid-tight manner except for leakage losses. One area is the space 26 connected to the high-pressure source, the second area has a step-like taper. It contains the second partial piston 23, which is displaceable in the taper immersed and delimits them in a liquid-tight manner from the rest of the second region, which forms the rear space 27. The area delimited by the partial piston 23 forms the high pressure chamber 28 of the pressure booster device connected to the pressure chamber 17 of the injection valve, which is connected via a check valve 29 and a fuel line 43 to the line 4 leading to the high-pressure fuel source 2. The two sub-pistons are separate components, but can also be designed to be firmly connected to one another. The second sub-piston 23 has at its end facing the first sub-piston a spring hanger 24 projecting beyond its diameter, so that the return spring 25 tensioned against the housing 20 presses the second sub-piston against the first.

The pressure of the high-pressure fuel source 2 is fed via 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 present in chamber 26, at valve 8, via valve 8 and line 42 in rear chamber 27, via valve and line 41 in closing pressure chamber 12 and via line 43 in high pressure chamber 28 and in pressure chamber 17. Thus, all pressure spaces of the pressure intensifier are subjected to rail pressure and the pressure intensifier piston is pressure-balanced, that is, the pressure intensifier is deactivated and there is no pressure boosting. In this state, the pressure booster piston is returned to its starting position via a return spring. The high-pressure chamber 28 is filled with fuel via the check valve 29. 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. The rail pressure can therefore be constantly present in the pressure chamber 17 without the injection valve opening unintentionally. The fuel is metered into the combustion chamber 5 by activating the 3/2-way valve 8, that is, by moving the valve into 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 transmission device, the two-part piston compresses the fuel in the high-pressure chamber 28, so that the pressure force acting in the opening direction increases in the pressure chamber 17 connected to the high-pressure chamber. At the same time, when the valve is transferred to its second position, the fuel pressure in the closing pressure chamber 12 drops, so that the pressure force acting on the closing piston in the closing direction decreases. The value of the fuel pressure in the pressure chamber 17 which is necessary for the opening of the injection valve thus drops precisely at the point in time at which the injection valve is to be opened, and the needle region 15 of the closing piston gives this

Injection openings 9 are already free at a lower pressure in the pressure chamber 17 than would be the case if the pressure in the closing pressure chamber 12 remained constant. As long as the rear space 27 is relieved of pressure, the pressure booster device remains activated and compresses the fuel in the high pressure space 28. The compressed fuel is passed on 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 and the pressure space 17 from the return line 44 and connects them 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 now also present again in the pressure chamber 17, the closing piston is hydraulically balanced and is closed by the force of the spring 11, as a result of which the injection process is ended. After the pressure equalization of the system, the pressure booster piston is inserted into its by a return spring

Starting position reset, the high pressure chamber 28 over the check valve 29 and the line 43 is filled from the high-pressure fuel source.

In an alternative embodiment, the closing pressure chamber can also be connected directly to the valve 8 via a fuel line instead of indirectly via the rear chamber 27 of the pressure booster device, i.e. instead of a line 41 connected to the rear chamber, a line is provided which leads directly from the closing pressure chamber to the valve 8 ,

Figure 2 illustrates the course of the fuel pressures p as a function of time t and the resulting stroke h of the closing piston during an injection cycle. The pressure of the high-pressure fuel source is denoted by prail, the pressure in the pressure chamber 12, at which the injection valve opens, by pö. The maximum stroke length of the injection valve is abbreviated to hmax, the maximum fuel pressure achievable in high-pressure chamber 28 to pmax. Curve 310 shows the time course of the fuel pressure in the high-pressure room or in the pressure room, curve 320 the pressure course in the closing pressure room.

If the valve is moved from the first to the second position at the time to, the pressure 310 im increases

High-pressure chamber and in the pressure chamber, starting from the pressure of the high-pressure fuel source, up to the maximum achievable pressure pmax, which is determined by the ratio of the

Cross-sectional areas of the two pistons and the pressure of the high-pressure fuel source is predetermined. At the same time, the pressure 320 in the closing pressure chamber drops to a low pressure value (the fuel pressure prevailing in the low-pressure system, not shown in any more detail). The injection valve opens, that is to say the stroke value h changes from zero to the value hmax as soon as the pressure forces acting in the opening direction in the pressure chamber 17 are the sum of the pressure forces acting in the closing direction in the closing pressure chamber 12 and overcompensate the force of the return spring 11. This is the case when the fuel pressure in the pressure chamber (see pressure curve 310) assumes the value pö. At a later time t1, the valve 8 is moved back into its first position, as a result of which the fuel pressures in

Bring the pressure chamber and closing pressure chamber closer to each other until they both reach the value of the fuel pressure of the high-pressure fuel source again. The valve closes again, i.e. the stroke value h returns to zero.

FIG. 3 shows a fuel injection device in which the same components as in FIG. 1 are provided with the same reference symbols. In contrast to Figure 1, the check valve is not via a line 43 with the

High-pressure fuel source, but connected to line 41 via line 70.

In contrast to FIG. 1, when the valve 8 is transferred from the second to the first position, the high-pressure chamber is not filled directly from the high-pressure fuel source, but from the rear chamber 27 and / or the closing pressure chamber 12.

In further alternative designs, the line 70 can also be connected directly to the rear space 27 or to the closing pressure space 12 instead of the line 41.

The 3/2-way valve 8 contained in the arrangements according to FIGS. 1 and 3 can be designed both as a magnetically and as a piezoelectrically controllable valve according to FIG. 4. In the piezoelectric embodiment according to FIG. 4, a valve housing 50 is connected to the three connecting lines 42, 44 and 45 known from FIGS. 1 and 3. In the valve housing there is a movably mounted valve body 51 which, in the rest position shown, has a return spring 52 which is between it and the valve housing is tensioned, is pressed with its hemispherical side surface in a liquid-sealing manner against the first valve seat 53. The opposite side of the valve body, which is formed by a flat surface, faces the second valve seat 54 connected to the line 45. In the rest position shown, there is a space between the valve body and the second valve seat. A pipe 55 leads from the first valve seat 53, to whose end facing away from the valve body the low-pressure line 44 is connected. A first power transmission piston 56 rests on the hemispherical side surface of the valve body which seals the tube and projects out of the tube through a sealed opening in the side wall of the tube facing away from the valve body, 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 coupling fluid. On the opposite side of the coupling space, a second power transmission piston 57 projects into the coupling space. The latter is fastened to an electrically controllable piezo actuator 59, which can change in length by applying an electrical voltage, a base element 60 fastened on the opposite side of the piezo actuator being at the same distance from the coupling space in every electrical state of the piezo actuator.

The position of the valve body shown is the first position of the 3/2-way valve. In this state, the valve body closes the connection of the tube to the space in which the valve body is movably mounted, so that the line 42 can only exchange fuel with the line 45. If the valve is to be moved into its second position in order to achieve a metering of fuel into the combustion chamber, the piezo actuator 59 must be electrical - left

can be controlled. To compensate for temperature-dependent changes in length of the piezo actuator and, with a suitable design of the coupling space 58, which is only shown schematically, also for force / displacement translation, the piezo actuator is in contact with the force transmission piston 56 via the force transmission piston 57 and the coupling space 58. If the piezo actuator is actuated, it expands, and a force is transmitted through the coupling space to the valve body, which lifts it from the first valve seat and presses it against the second valve seat, so that now line 45 is used instead of line 44 the line 42 is connected.

As shown in FIGS. 1 and 3, the piezo valve can be connected to line 4 by means of line 45. Alternatively, the valve can also be connected directly to the space 26 instead of the line 4.

FIG. 5 illustrates a further embodiment with one integrated in the injector housing 100

Pressure booster device. The same components as shown in Figures 1 and 3 are given the same reference numerals and will not be described again. In the injector housing, three parts that are movable relative to one another are spring-mounted: a pressure booster piston 121, a closing piston 113 and a hollow valve piston 206. The pressure booster piston 121 has a first partial piston 122 and a second partial piston 123. The first partial piston 122 is guided axially liquid-tight from the injector housing except for leakage losses. On one side, the first partial piston has a step-shaped taper, so that the return spring 125 of the pressure transmission device can be accommodated between the injector housing and the first partial piston. The return spring 125 is between a spring retainer 124 arranged on the taper and an am

Injector housing attached limiting element 200 tensioned, the side of the return spring facing away from the Boundary element as a stop for the

Pressure intensifier piston serves to prevent the tapering of the first partial piston from being pushed against the injector housing. The space 126 between the first piston and the injector housing, in which the return spring 125 is located, corresponds to the space 26 from FIG. 1 and is connected to the high-pressure fuel source 2 via the line 4. The first sub-piston 122 merges on the side facing away from the space 126 into the second sub-piston 123, which has a smaller diameter, which also extends in regions

Injector housing is guided, since this has a step-shaped taper in the region of the second piston. The space between the second partial piston and the injector housing forms the rear space 127 of the pressure booster, which extends through bores 141 in the second

Partial piston is connected to its hollowed out inner area forming the closing pressure chamber 112. The closing piston 113 projects into the closing pressure chamber; the opposite end of the closing piston, the needle region 115, closes the injection openings 9

In the area of the closing piston projecting from the closing pressure space and the needle area, there is the guide area 114 of the closing piston, which ensures axial guidance of the closing piston along the injector housing. The guide area is larger in diameter than the needle area. The guide area has a flow connection 205, for example in the form of a continuous bore, so that the space between the needle area and the injector housing and the smaller diameter area of the closing piston adjoining the guide area beyond the needle area can exchange fuel with one another. Between the guide area 114 and the area of the closing piston projecting into the closing pressure space, a circular ring piece 203 is attached to the circumference of the closing piston, which protrudes into a cylindrical symmetrical bulge 202 of the injector housing without being able to touch the housing. The circular ring piece 203 serves to support the Return spring 111, which presses the closing piston against the injection openings. For this purpose, the return spring 111 rests on a radial projection of the hollow valve piston 106 which is guided by the closing piston and does not touch the injector housing. The hollow valve piston has an end tapering to a circular sealing edge, which is pressed by the return spring 111 against the end face of the second partial piston, so that the high-pressure space 128, which is formed by the space located beyond the hollow valve piston between the closing piston and the injector housing, can be sealed against the closing pressure chamber 112, that is to say that the hollow valve piston together with the end face of the second partial piston can serve as a check valve 129. Bores 204 are made in the circular ring piece 203, which support the fuel exchange between the regions of the high-pressure space on both sides of the circular ring piece. Between the annular piece and the end of the needle area facing the injection openings, the closing piston has two areas with a diameter that is smaller than the diameter in the area projecting into the closing pressure space: on the one hand, a waist between the guide area and the annular piece, and on the other hand the area between the guide area and the end of the closing piston facing the injection openings.

In the arrangement according to FIG. 5, 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 mode of operation is otherwise similar to that of the arrangement according to FIG. 1. The check valve for filling the high-pressure chamber 128 is formed by the check valve 129 described above. The fuel is also metered into the combustion chamber 5 by activating the 3/2-way control valve 8. This relieves pressure in the rear chamber 127 and the closing pressure chamber 112 and activates the pressure booster. The fuel in the high-pressure chamber 128 is compressed and via the flow connection 205 Injector tip forwarded. As a result of the pressure drop in the closing pressure chamber, the pressure required for lifting the closing piston drops below the value that would be required if the pressure in the closing pressure chamber remained constant. The closing piston finally releases the injection openings as a result of the increasing opening pressure force in the high-pressure chamber and the simultaneously decreasing closing pressure force in the closing pressure chamber, and the fuel is injected into the combustion chamber. The hollow valve piston 206 seals the high-pressure chamber 128 with a guide with respect to the closing piston, the hollow valve piston being axially displaceable and moving together with the pressure booster piston toward the injection openings during the compression of the fuel in the high-pressure chamber. As already stated, the

Hollow valve piston from the high pressure chamber with its sealing seat opposite the second partial piston. This ensures that no compressed fuel can flow back into the closing pressure chamber. To end the injection, the control valve 8 separates the rear space 127 from the line 44 and connects it to the high-pressure fuel source 2, as a result of which the rail pressure builds up in the rear space and in the closing pressure space and the pressure in the high-pressure space drops to rail pressure. The closing piston is now hydraulically balanced and is closed by the force of the return spring 111, which ends the injection process. As a result of the pressure equalization, the pressure booster piston 121 is now also returned to its starting position by the return spring 125, the high-pressure chamber 128 being filled via the check valve 129 from the closing pressure chamber 112 or the rear chamber 127.

To stabilize the switching sequences, additional structural measures for damping any vibrations that may occur between the high-pressure fuel source and the injector can be taken. In addition to a suitable one The design of throttle 3 can also be installed alternatively or in combination with throttle check valves at any point on supply lines 4, 42 and 45. The holes 204 can also be omitted. In addition, the pressure booster piston, the closing piston and the

Hollow valve pistons also have different shapes. The only thing that is essential for the locking piston is that, on the one hand, a fuel supply is guaranteed up to the injection openings and that in the area of the high-pressure chamber the fuel pressure has a contact surface which effectively leads to an axial force on the locking piston which is oriented towards the pressure booster piston, that is to say acts in the opening direction.

In all exemplary embodiments, the closing pressure chamber 12 or 112 and the rear chamber 27 or 127 are realized by a common closing pressure rear chamber (12, 27, 41) or (112, 127, 141), with all sub-areas (12, 27) or (112, 127) of the closing pressure rear space are permanently connected to one another for the exchange of fuel, for example via at least one fuel line 41 or via at least one bore 141 integrated in the pressure booster piston. The pressure space 17 and the high pressure space 28 can also be connected by a common injection space (17, 28, 40) are formed, with all subregions of the injection chamber being permanently connected to one another for the exchange of fuel. The pressure chamber 17 and the high-pressure chamber 28 can be connected to one another via a fuel line 40 (compare FIGS. 1 and 3), or the pressure chamber can be formed by the high-pressure chamber (128) itself (see FIG. 5).

FIG. 6 shows the time profiles of the fuel pressure p in the high-pressure chamber 28 or 128 for different switching speeds of the 3/2 piezo valve of FIG

Curve 310 shows the pressure conditions when the piezo valve is actuated quickly, curve 311 when the valve actuation is slow. The first position of the valve, in which the valve body is pressed against the first valve seat 53, becomes 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. When the valve is actuated quickly, the piezo actuator is electrically controlled such that the valve body quickly moves from the rest position to the end position; when the valve is actuated slowly, the electrical voltage applied to the piezo actuator is slowly increased so that the valve body moves from the rest position to the end position at low speed. Curves 320 and 321 show the associated pressure profiles in the rear space of the pressure booster as a function of time t. The resulting stroke h of the piezo actuator, that is to say the movement of the valve body, is shown in curves 330 and 331. Prail denotes the pressure of the high-pressure fuel source or the pressure in the high-pressure rail of the common rail system, pmax the maximum in

High pressure space achievable fuel pressure and hmax the maximum stroke of the valve body.

In the rest position of the valve body, the pressure booster is deactivated and the piston of the pressure booster is in its

Initial position reset, there is no injection. Rail pressure prail prevails in both the high-pressure chamber and the rear chamber (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 intensifier is fully activated, the pressure in the rear area drops to a small value close to zero and the pressure in the high pressure room reaches its maximum value pmax. The closing piston is raised and an injection takes place. In a transition area between the rest position and the end position, the pressure intensifier is partially activated, the pressure in the rear space decreases with increasing stroke of the piezo valve and the pressure intensifier piston generates an average injection pressure that increases with increasing valve stroke, so that the injection takes place with increasing pressure. The diagrams shown in FIG. 6 simplify the process

Representation assumed that the nozzle opening pressure differs only slightly from the rail pressure. When the valve is actuated slowly from time t1 (curve 331), the pressure in the rear space drops continuously to time t2 to a small value (curve 321), while the pressure in the high pressure room slowly increases to pmax (curve 311). When the nozzle opening pressure is reached shortly after tl, the closing piston lifts off the injection openings 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 have been reached. The closing process at time t3 takes place quickly in order to ensure a rapid reduction in pressure at the end of injection (the term "rapid spill" is used for this in English technical term). So at time t3, in which the

If the extension of the piezo actuator is reversed, the pressure in both the high-pressure chamber and in the rear chamber is returned to the rail pressure level and the closing piston closes the injection openings again. If, on the other hand, the valve is actuated quickly at time t1 (curve 330), the transition area is passed quickly and the pressure in the high-pressure chamber rises to the maximum level pmax considerably before time t2 (see curve 310), while the pressure in the rear chamber quickly increases to one low value drops (see curve 320). Accordingly, a quasi-rectangular pressure curve 310 results. The closing process takes place quickly, in an analogous manner to the previously described case, in order to ensure rapid pressure reduction at the end of injection.

FIG. 7 shows the pressure conditions in the event that, for example, the piezo valve according to FIG. 4 is operated as a 3/3-way valve. In addition to the rest position and the end position, the valve body of the valve in this case also has a central position in which it can remain at least for a certain period of time and in which line 42 is connected to both line 45 and line 44. Then, during this period, a pressure equilibrium can be established in the rear space at an intermediate pressure level PZ1, which is due to the one flowing off into the low pressure system and that of the

High-pressure fuel inflow amount is determined together. Curve 410 shows the pressure curve in the high-pressure chamber, curve 420 the pressure curve in the rear chamber. In the h (t) diagram below, the time course of the stroke of the closing piston is in the third diagram, the time course of the Piezohubs H, i.e. the movement of the valve body, shown. Hmax denotes the maximum value for the piezo stroke with which the end position of the valve body can be set, in which the rear chamber 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, tl to t5 denote various successive points in time within an injection cycle which comprises a boat injection, i.e. a first injection phase at a low pressure level, and a second injection phase at a high pressure level.

At time t1, the valve body is moved into the middle position by a corresponding control of the piezo actuator and held in this middle position until time t3 (see the H (t) diagram). The pressure in the back area drops

Intermediate pressure level PZ1 decreases while the pressure in the high-pressure chamber slowly increases. 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 pressure value that can be achieved with the pressure intensifier. At time t3, the piezo valve is moved into its end position (second position) with the stroke value Hmax, so that the pressure in the rear space drops to a low value close to 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 space 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 an injection with a low injection pressure, with the intermediate position again going into the rest position. This happens, for example, with small injection quantities, such as those required for a pre-injection or at idle.

FIG. 8 shows a modification of the embodiment according to FIG. 3, in which, with an otherwise identical construction, a throttle 520 in the line 70 is installed, so that the connection between the high pressure chamber 28 and the closing pressure chamber 12 or the rear chamber 27 is throttled. The cross section of the connecting path of the 3/2-way valve 8 between the line 45 and the line 42 is provided with the reference number 510 and is referred to below as the valve cross section.

A suitable adjustment of the valve cross-section 510, which connects the rear space 27 to the pressure supply, and the flow cross-section of the filling path 70, by a suitable choice of the flow cross-section of the throttle 520, can generate an additional hydraulic force for closing the needle. For this purpose, the filling path 70 is designed to be very small by the throttle 520, but large enough to fill the high-pressure chamber 28 and reset the pressure booster piston to the next one

To enable injection. Furthermore, the valve cross section 510 is designed large enough so that a rapid pressure build-up to rail pressure takes place in the rear space 27, and depending on the line design, a pressure increase in the rear space can also take place. As a result of the rapid build-up of pressure in the rear space, the pressure in the high-pressure space 28 is rapidly reduced to rail pressure with subsequent pressure undershooting under rail pressure. The throttle 520 prevents a too rapid pressure equalization between room 28 and room 12 or 27. Since rail pressure is still present in the closing pressure chamber 12 in this phase, a closing hydraulic force occurs on the nozzle needle.

In a further alternative embodiment, the design of the flow cross section of the filling path 70 is ensured by a check valve 29 having a corresponding flow cross section instead of using a throttle.

FIG. 9 schematically shows the pressure profiles that can be achieved with the arrangement according to FIG. 8. Here, the time course of the fuel pressure in the high-pressure chamber 28 is identified by the reference number 1310 provided, the time course of the fuel pressure in the rear space 27 of the pressure booster with the reference number 1320.

Here, the end of injection is represented as follows: after valve 8 is deactivated, it takes place in the rear space 27 and

Closing pressure chamber 12 a pressure build-up to rail pressure, whereby at the same time there is a rapid pressure drop to rail pressure in the high pressure chamber 28. The latter drop in pressure occurs so quickly that the pressure in the high-pressure chamber and in the pressure chamber of the injector sinks below the rail pressure. It is precisely in this phase that the needle closes, so that an additional hydraulic pressure force acts on the nozzle needle, as a result of which the needle closes quickly and the amounts of fuel can be metered into the combustion chambers of the internal combustion engine more precisely. In the further course, the rail pressure also arises in the high pressure room and in the pressure room. The overshoot drawn in the course of 1320 beyond the rail pressure is hydraulic 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 room is the rapid build-up of pressure in the back room.

Figure 10 shows a modified embodiment of the arrangement shown in Figure 3. In this case, instead of line 45, a fuel line 1450 is provided, which is not connected directly to line 4, but to the space of the pressure booster into which line 4 opens. The line 1450 opens into the room at the end of the pressure booster chamber opposite the line 4. Furthermore, the line 41 from FIG. 3 is replaced by a fuel line 1410 which, in contrast to the line 41 from FIG. 3, opens into the rear space 27 beyond the mouth of the line 42 in the rear space 27. Furthermore, this line 1410 is connected to the closing pressure chamber 12 in such a way that a line 1700 replacing the line 70 from FIG. 3 can be fastened diametrically opposite to the opening in the closing pressure chamber. The other end of the line 1700 is connected to the high-pressure chamber 28 in a manner known from FIG. 3 via a check valve 29. Furthermore, line 40 from FIG. 3 is replaced by line 1400, which is diametrical opposite the line 1700 or the check valve 29 opens into the high pressure chamber 28. In contrast to the arrangement according to FIG. 3, a limiting element 2000, which limits the opening stroke of the injector, is also fastened in the closing pressure chamber.

The mode of operation is essentially the same as that of the arrangement according to FIG. 3, with the difference that the diametrical arrangement of the mouths of the fuel lines in the spaces of the pressure intensifier or in

Closing pressure chamber of the injector the rooms flushing all rooms with fuel is required.

Claims

Expectations

1. Fuel injection device for internal combustion engines with a fuel injector that can be supplied by a high-pressure fuel source, a movable one between the fuel injector and the high-pressure fuel source

Pressure booster piston having a pressure booster piston is connected, the pressure booster piston separating a space which can be connected to the high-pressure fuel source from a high-pressure space connected to the fuel injector, the fuel pressure in the high-pressure space being able to be varied by filling a back space of the pressure booster device with fuel or by emptying the back space of fuel, the Fuel injector has a movable closing piston for opening and closing injection openings, the closing piston (13; 113) in one

Closing pressure chamber (12; 112) protrudes so that fuel pressure can be applied to the closing piston to achieve a force acting on the closing piston in the closing direction, and that the closing pressure chamber (12; 112) and the rear chamber (27; 127) by a common closing pressure rear chamber (12, 27, 41; 112, 127,

141) are formed, with all partial areas (12, 27; 112, 127) of the closing pressure rear space being permanently connected (41; 141) for the exchange of fuel, with a pressure space (17; 128) for supplying the injection openings with fuel and To act upon the closing piston with a force acting in the opening direction, characterized in that the high-pressure chamber (28) is connected to the high-pressure fuel source in such a way (43; 70, 41, 42; 1700, 1410, 42) that apart from the high-pressure chamber of pressure fluctuations, constantly at least the fuel pressure of the

High-pressure fuel source can be applied, the pressure chamber and the high-pressure chamber being formed by a common injection chamber, all subregions of the injection chamber being permanently connected to one another for the exchange of fuel.

2. Fuel injection device according to claim 1, characterized in that the pressure chamber (17) and the high pressure chamber (28) are connected to one another via a fuel line (40).

3. Fuel injection device according to claim 1, characterized in that the pressure chamber is formed by the high pressure chamber (128).

4. Fuel injection device according to one of the preceding claims, characterized in that the closing pressure chamber

(12) and the rear space (27) are connected to one another via a line.

5. Fuel injection device according to one of claims 1 to 3, characterized in that the closing pressure chamber (112) and the rear chamber (127) are delimited from one another by a partial piston (123) of the pressure booster piston (121), at least one of the closing pressure chamber and bore (141) connecting the rear space is introduced.

6. Fuel injection device according to one of the preceding claims, characterized in that the high-pressure chamber (28) is connected (43) to the chamber (26) via a check valve (29).

7. Fuel injection device according to one of claims 1 to 5, characterized in that the high pressure chamber (28; 128) with the closing pressure chamber (12; 112) is connected (70).

8. Fuel injection device according to claim 7, characterized in that the connection (70) is a check valve

(29; 129) contains.

9. Fuel injection device according to claim 7 or 8, characterized in that the connection between the high pressure chamber (28) and the closing pressure chamber (12) is throttled (520; 29) such that during a closing process Undershoot of the pressure in the pressure chamber can take place below the pressure of the high-pressure fuel source.

10. Fuel injection device according to one of the preceding claims, characterized in that the rear space (27; 127) via a valve (8) can optionally be connected to a low-pressure line (44) or to the high-pressure fuel source (2).

11. Fuel injection device according to claim 10, characterized in that the valve a first and a second

Position valve is, the piezo valve, the rear space in a first position with the

High pressure fuel source and in a second position with the low pressure line (44).

12. Fuel injection device according to claim 11, characterized in that the piezo valve is designed such that the speed of the transition between the first and the second position can be varied.

13. Fuel injection device according to one of claims 10 to 12, characterized in that the valve can be transferred into at least one intermediate position, so that there is an intermediate pressure level in the rear space.

14. Fuel injection device according to claim 13, characterized in that the valve in the intermediate position connects the rear space both with the high-pressure fuel source and with the low-pressure line.

15. Fuel injection device according to one of the preceding claims, characterized in that in at least one of the rooms (26, 27, 28) of the pressure transmission device and / or in the closing pressure chamber (11) of the fuel injector in the room or in the rooms opening lines (4, 1450; 42, 1410; 1410, 1700; 1700, 29, 1400) are arranged in this way, in particular are arranged diametrically opposite one another, so that in the event of a fuel flow in the lines, the room or rooms are forced to be flushed with fuel.