KR20030017634A - Fuel injection device - Google Patents

Abstract

A fuel injector for an engine having a fuel injector and a pressure intensifier that can be supplied from a high pressure fuel source is proposed, the pressure intensifier comprising a movable pressure intensifier piston that separates a chamber connectable to the high pressure fuel source from a high pressure chamber connected with the fuel injector. Wherein the fuel pressure in the high pressure chamber may be changed through fuel filling of the return chamber of the pressure intensifier and fuel discharge of the return chamber, the fuel injector including a movable closing piston for opening and closing the injection opening, By closing the closing piston into the closing pressure chambers 12, 112, the closing piston can be pressurized by fuel pressure to form a force acting on the closing piston in the closing direction, and with the closing pressure chambers 12, 112. The chambers 26, 126 are configured through a common working chamber and all partial regions 12, 47, 26, 112, 130, 126 of the working chamber. Are permanently connected to each other (47, 130) for fuel exchange.

Description

FUEL INJECTION DEVICE}

German Patent No. 43 11 627 discloses a fuel injector in which the integral pressure enhancing piston enables fuel injection pressure above the value provided from the common rail system using the filling or emptying of the storage chamber.

The present invention relates to a fuel injection device according to the preamble of the independent claim.

Embodiments of the invention are shown in the drawings and described in detail below.

1 is a view of a fuel injection device.

2 is a view of a piezo valve.

3 is a view of a fuel injection device.

4 is a view of another fuel injection device.

5 is a diagram of two graphs.

6 is a diagram of three different graphs.

7 illustrates another alternative embodiment.

8 is a pressure graph for the structure according to FIG.

The fuel injection device according to the invention with the features of the independent claims furthermore loses control in the high pressure fuel system based on the control via the return chamber of the pressure booster compared to the timely control of the operating chamber connected with the fuel high pressure source. It has the advantage of being small. In addition, the high pressure region, in particular the high pressure chamber, is depressurized only to the rail pressure and not to the leak level, thereby improving hydraulic efficiency.

By means described in the dependent claims, a preferred configuration and improvement of the fuel injection device described in the independent claims is possible.

The coaxial arrangement of the pressure boosters relative to the closed piston preferably permits a small space and low cost configuration.

When the pressure chamber function of the injector is taken over by the high pressure chamber of the pressure intensifier, a reduced dead space is formed at the rear of the pressure intensifier that must be sealed at high pressure. In addition, the amplitude of the vibrations that occur in some cases between the closed pressure chamber and the pressure chamber is reduced because shorter flow connections are formed. Thus, a reliable operation with an overall faster switchability is formed.

By using a rapidly switching piezo valve as a control valve, even a high nozzle opening pressure can be injected into the combustion chamber of the engine in a prescribed manner and with a small injection rate tolerance. In addition, only a small leak loss occurs due to the rapid switching process.

In practice, in particular piezo valves with linearly controllable piezo actuators, the switching speed variability allows for a change in the pressure rise at the start of the injection, ie the optimum adaptation of the injection process to the type of injection process and the needs of the engine.

If a 3 / 3-way piezo valve is used, an intermediate position through a partial stroke of the piezo actuator is realized, allowing for injection even at low pressures. In addition, the boot injection can improve the supply of a small amount of fuel.

In particular, improved needle closure can be achieved through optimum hydraulic adjustment of the filling path of the high pressure chamber. In addition, an acceleration phase is formed in which the pressure in the nozzle chamber is lower than the pressure in the needle pressure chamber. Thus, additional hydraulic closing force on the nozzle needle is formed, and the acceleration phase upon closing can be significantly shortened. As the needle closes faster, the fuel quantity-characteristic curve becomes flatter during load operation. This additional hydraulic force achieves very stable needle closing force and injection termination. This increases the supply accuracy of the injector. In addition, a faster response of the nozzle needle to the control signal end is achieved, so that a flatter fuel amount-characteristic curve is achieved in the load range, thereby further increasing the supply accuracy. At the same time, improvement of the exhaust emission value of the engine is considered through faster needle closure.

Other advantages can be seen from the features described in the other dependent claims and the detailed description.

In FIG. 1, a fuel injector 1 comprising a pressure intensifier 7 is connected to a high pressure fuel source 2 via a fuel line 4, and a throttle 3 on the fuel high pressure source side within the fuel line 4. The fuel injection valve is shown on the injector side and on which the check valve 19 is connected in parallel with the second throttle 18. The fuel high pressure source comprises a number of elements not shown in detail, such as fuel tanks, pumps and high pressure rails of known common rail systems, the pump provides a high fuel pressure of 1600 bar to the high pressure rail, and the pump supplies fuel to the tank From the high pressure rail. Each cylinder of the engine is provided with a separate injector provided from the high pressure rail. The injector 1 illustrated by way of example in FIG. 1 comprises a fuel injection valve 6 with a closed piston 13, which through the injection opening 9 into the combustion chamber 5 of the cylinder of the engine. Extrude The closing piston 13 is surrounded by the pressure chamber 17 at the pressure shoulder 16, which is connected to the high pressure chamber 28 of the pressure intensifier 7 via the high pressure line 40. The closing piston 13 projects in the guide region 14 at the opposite end of the combustion chamber, through line 47, into the closed pressure chamber connected with the chamber 26 of the pressure intensifier connected with the fuel high pressure source. The return chamber 27 of the pressure intensifier can be connected to the high pressure fuel source 2 via fuel lines 42, 45 and a 3/2 way valve 8. The valve 8 connects the line 42 and the line 44 in a first position, but the low pressure line 44, which is led to a low pressure system not shown in detail, is connected to the end of the low pressure line connected to the valve 8. . The line 42 leading to the return chamber 27 in the second position of the valve is connected with the low pressure line 44, but the end of the line 45 opposite the high pressure fuel source 2 which is connected to the valve is closed. The closing piston is placed in a closed pressure chamber and is spring loaded by a return spring 11 tensioned between the housing 10 of the injection valve 6 and the closing piston 13, the return spring being the injection opening ( The needle region 15 of the closing piston is pressed against 9). The pressure intensifier 7 includes a pressure intensifier piston 21 positioned in a spring loaded manner, the pressure intensifier piston being connected to a high pressure chamber 28 connected to a high pressure line 40 via a line 4 of a high pressure fuel source. It is separated from the chamber 26 connected with (2). The spring 25 used for the support of the piston is arranged in the return chamber 27 of the pressure intensifier. The piston 21 consists of two parts and comprises a first partial piston 22 and a second partial piston of smaller diameter. The housing 20 of the pressure intensifier is divided into two zones which are fluidically separated from one another until a leak is lost by means of a partial piston 22 displaceably disposed within the housing. The first region is the chamber 26 connected with the high pressure source and the second region has a stepped taper. The second region includes a second partial piston 23 slidably entering the taper and hydraulically closes the taper from the remaining portion of the second region that forms the return chamber 27. The tapered region defined by the partial piston 23 forms a high pressure chamber 28 of the pressure intensifier, which is connected with the pressure chamber 17 of the injection valve, which comprises a check valve 29 and a fuel line 49. It is connected with the line 47 or the closed pressure chamber 12 through. The two-part piston may be separate components or may be configured to be fixedly coupled to each other. The second partial piston 23 includes a spring fixture 24 protruding beyond its diameter at its own end facing the first partial piston, so that the return spring 25 tensioned against the housing 20 is removed. Press the two partial piston against the first partial piston.

The pressure of the high pressure fuel source 2 is supplied to the injector via line 4. In the first position of the valve 8 the injection valve is not controlled and no injection is made. Rail pressure is then applied to the chamber 26 and the valve 8, through the valve 8 and the line 42 to the return chamber 27 and the closed pressure chamber 12, the check valve 29 Is applied to the high pressure chamber (28) and the pressure chamber (17) via a line (49). As such, all pressure chambers of the pressure intensifier are pressurized by rail pressure, such that the pressure intensifier piston is pressure balanced, which means that the pressure intensifier is deactivated and the pressure is not increased. In this state, the pressure increasing piston is restored to the original position by the return spring. The high pressure chamber 28 is filled with fuel by the check valve 29. Hydraulic closing force is exerted on the closing piston via the rail pressure in the closing pressure chamber 12. In addition, the return spring 11 provides a closed tension. In this way, the rail pressure can always be maintained in the pressure chamber 17 without the unwanted opening of the injection valve. When the pressure in the nozzle chamber achieved by the connection of the pressure booster increases above the rail pressure, the nozzle needle is opened to inject the spray. The fuel supply into the combustion chamber 5 is performed through the activation of the 3/2 way valve 8, ie by switching the valve to the second position. Thus, the return chamber 27 is disconnected from the high pressure fuel source and connected to the return line 44, and the pressure in the pressure chamber is lowered. This activates the pressure intensifier and the two parts of the piston compress the fuel in the high pressure chamber 28 so that the pressure acting in the open direction in the pressure chamber 17 connected with the high pressure chamber increases and the closed piston opens the injection opening. Open it. While the pressure chamber 27 is depressurized, the pressure intensifier is activated to compress the fuel in the high pressure chamber 28. The compressed fuel continues to be guided to the injection openings and injected into the combustion chamber. At the end of the injection, the valve 8 is switched back to the first position. This separates the pressure chamber 27 from the return line 44 and connects the pressure chamber again with the supply pressure of the high pressure fuel source or the rail pressure of the common rail system. Through this, the pressure in the high pressure chamber falls to the rail pressure, which is likewise re-formed in the pressure chamber 17 so that the closing piston is hydraulically compensated and closed by the force of the spring 17 to inject Ends. After the pressure balance of the system, the pressure boosting piston is returned to its initial position by a return spring, and the high pressure chamber 28 is filled by a check valve 29 and a line 49 from the high pressure fuel source. A check valve 19 connected in parallel with the throttle 3 or the throttle 18 is used for vibration damping between the high pressure fuel source and the injector, the vibration being needle closed, in particular a multi-injection, ie short closing, which is carried out in some cases. And may adversely affect the opening process.

In alternative embodiments, the check valve 29 may be integral to the pressure enhancing piston. Since the check valve 29 can be connected to the return chamber 27 instead of the closed pressure chamber 12 in the separated configuration as well as in the integral configuration, the high pressure chamber is filled when the injection valve is closed. Is performed from the check valve 27 instead of the closed pressure chamber 12. Throttles 3 and 45 used for vibration damping (throttle 45 in parallel with the check valve) can be mounted at any position between the high pressure fuel source and the chamber 26 of the detector. Other pressure intensifiers can be used that can be controlled through the return chamber. For example, another pressure intensifier can be used in which a two-part pressure intensifier piston is controllable via the return chamber, in which a check valve necessary for filling the high pressure chamber is integrated into the (small diameter) second part piston.

The three-way valve 8 included in the structure according to FIGS. 1 and 3 may be configured as an electronically or piezoelectrically controllable valve according to FIG. 2. In the piezo embodiment as a 3/2 way valve according to FIG. 2, the valve housing 50 is connected with the three connection lines 42, 44, 45 shown in FIG. 1. Within the valve housing is a valve body 51 which is movably supported, the valve body being fluidically sealed with a semi-circular side by a return spring 52 which is tensioned between the valve body and the valve housing in the shown stop position. Is pressed against the first valve seat 53. The opposite side of the valve body formed in the plane faces the second valve seat 54 connected to the line 45. In the stop position shown, an intermediate chamber is provided between the valve body and the second valve seat. A conduit 55 is guided from the first valve seat 53, and a low pressure line 44 is connected to the end opposite the valve body. The first force transmission piston 56 lies on the semi-circular side of the valve body that seals the conduit and projects from the conduit through a closed opening in the conduit side wall opposite the valve body such that force is directed from the outside of the valve housing to the force transmission piston. Displacement can be applied onto the valve body. The extended end piece of the piston is shown schematically and enters the coupling chamber 58 filled with a coupling fluid, for example fuel. The fuel used as coupling fluid is supplied, for example, from a low pressure system and from a low pressure system via a line not shown in detail. On the opposite side of the coupling chamber the second force transmission piston 57 enters into the coupling chamber. The second force transmission piston is fixed to an electrically controllable piezo actuator 59 whose length can be changed through the application of a voltage, and the bottom element 60 fixed to the opposite side of the piezo actuator is a piezo to the coupling chamber. There is an equal spacing in each electrical state of the actuator.

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 conduit and the chamber in which the valve body is located to move, so that the line 42 can exchange fuel with the line 45. When the valve is guided to the second position to supply fuel into the combustion chamber, the piezo actuator 59 must be electrically controlled. In order to compensate for the length change of the temperature-dependent piezo actuator and for force / direction in the appropriate configuration of the coupling chamber 58 schematically shown, the piezo actuator is provided with a force transmission piston 57 and a coupling chamber 58. Is in contact with the force transmission piston 56. When the piezo actuator is controlled, the piezo actuator is inflated so that a force is transmitted through the coupling chamber onto the valve body, which forces the valve body up from the first valve seat and presses it onto the second valve seat, thereby providing a line (45). ) Is no longer connected to line 42, and line 44 is connected to line 42.

As shown in FIGS. 1 and 3, the piezo valve is connected to line 4 by line 45. Alternatively, the valve may be connected directly to the chamber 26 instead of to the line 4. The valve body may have other forms, that is, it may be used in a piezo-operable slide valve, flat seat valve or conical valve or in any combination. If an intermediate position is provided between the first position and the second position, for example to slowly depressurize the return chamber and to correspondingly slowly build the fuel pressure in the high pressure chamber, a valve that does not have an open overlap of the two valve seats It may be preferred to be used as a switching valve, for example, before the first valve seat opens slowly, the second valve is first closed. This reduces fuel loss when the valve switching in the switching area is slower because there is no connection time from the rail to the return system. In addition, sliding seat valves may be used. The piezo actuator may consist of a three-third-way valve, in combination with slow control of at least one intermediate position of the valve body, optionally or staying for a period of time, by corresponding electrical control of the piezo actuator, eg For example, preliminary injection can be implemented at a constant low pressure level. Of course, connections to lines 44 as well as lines 42 and 45 at at least one intermediate position must be formed, whereby a constant pressure intermediate level can be formed in the return chamber and the high pressure chamber. The intermediate pressure level in the return chamber is determined through the flow cross section of the valve seats 53, 54. It is preferable that the flow cross section of the valve seat is configured to be larger than the flow cross section of the line 42 or conduit 55 and the intermediate pressure level is chosen so as to be determined only by the supply and shut off flow cross sections of the lines 42, 44, 45 Do. This results in the stroke region of the valve body having no influence on the value of the intermediate pressure level in the intermediate position. As such, the administrative tolerances of the piezo actuators in some cases do not affect the injection process.

3 shows another embodiment of a pressure intensifier device integrated in the injector housing 100. Like parts shown in FIG. Within the injector housing, three parts of the pressure enhancing piston 121, the closing piston 113 and the valve hollow piston 206, which are relatively movable relative to one another, are located spring loaded. The pressure intensifying piston 121 includes a first partial piston 122 and a second partial piston 123. The first partial piston 122 is guided by the injector housing hydraulically sealed until there is a leak loss. Since the first partial piston includes a stepped taper on one side, a return spring of the pressure intensifier is located between the injector housing and the first partial piston. The return spring 125 is tensioned between the spring fixture 124 disposed in the tapered portion and the limiting element 200 fixed to the injector housing, the limiting element side opposite the return spring having the tapered portion of the first partial piston injector It is used as a stop for the pressure enhancing piston to prevent it from crashing into the housing. The chamber 126 between the first partial piston and the injector housing, in which the return spring 125 is located, corresponds to the chamber 26 of FIG. 1 and is connected to the high pressure fuel source 2 via line 4. . The first partial piston 122 is connected to the first partial piston 123 having a smaller diameter on the opposite side of the chamber 126, and the second partial piston is partly guided by the injector housing as well, the housing being second This is because it has a stepped taper in the region of the partial piston. The chamber between the second partial piston and the injector housing forms a return chamber 127 of the pressure booster. The pressure intensifying piston consists of a hollow piston. The central through bore 130 of the pressure intensifying piston hydraulically connects the chamber 126 with the end of the closing piston 113 which is used as a closed pressure chamber and rushes into the hole end opposite the chamber 126. The opposite end of the closing piston and the needle region 115 close the injection opening 9. A guide region 114 of the closed piston, which ensures axial guidance of the closed piston along the injector housing, is located between the closed piston region and the needle region that have entered the closed pressure chamber, correspondingly the injector housing is It includes two stepped tapered portions. The diameter of the guide region is preferably larger than the diameter of the needle region. The guide region is penetrated by a flow connection 205 in the form of a through bore, for example, so that the intermediate chamber between the needle region and the injector housing and the small diameter of the closed piston are connected to the guide region on the opposite side of the needle region. The intermediate chamber between the housing and the housing can be fuel exchanged with each other. Return spring 131 presses the closing piston against the injection opening. The valve hollow piston includes an attachment to an end extending to the circular hermetic edge, the end being pressed against the front face of the second partial piston by a return spring 111, thereby closing the closing piston and injector housing on the opposite side of the valve hollow piston. The high pressure chamber 128, which is formed through the intervening chamber, can be closed against the closed pressure chamber 112, ie the valve hollow piston can be used as a check valve with the front side of the second partial piston. The closing piston includes two regions having a smaller diameter than the region entering into the closed pressure chamber, between the region entering into the bore 130 and the end of the needle region facing the injection opening. These two regions are on the one hand the recess between the guide region and the ingress into the bore and on the other hand the region between the closed piston end and the guide region facing the injection opening. In the injector housing 100, a gap piece 132 that rushes into the bore 130 in the form of a cylinder is fixed in the chamber region. On the side facing the closing piston, the gap piece 132 includes a tapered portion, and a closing chamber spring 131 is pressed against the closed piston spring to press the end of the closed piston into the bore 130, and the closing piston is injected into the injection opening. Sufficient free space is provided between the closing piston and the spacer piece so as to be lifted up from and to carry out the injection process. In forming the proper volume, the gap limits the stroke of the closing piston to the range required in the injection process.

In the apparatus according to FIG. 3, the high pressure chamber 28 and the nozzle chamber 17 of the apparatus according to FIG. 1 are formed by the high pressure chamber 128. Other functions are similar to the device according to FIG. 1. The check valve for filling the high pressure chamber 128 consists of the check valve 129 described above. The fuel supply into the combustion chamber 5 is likewise carried out via the operation of the 3 / 2-way control valve. Through this, the return chamber 127 is pressure released and the pressure booster is activated. The fuel in the high pressure chamber 128 is compressed and supplied to the injector through the connection 205. The closing piston opens the injection opening by rising open pressure in the high pressure chamber, and fuel is injected into the combustion chamber. Therefore, the injection pressure is higher than the rail pressure from the beginning. The valve hollow piston 206 closes the high pressure chamber 128 using a guide to the closing piston, the valve hollow piston being axially displaceable and in the direction of the injection opening with the pressure enhancing piston during compression of the fuel in the high pressure chamber. Move. As described above, the sealing seat of the valve hollow piston closes the high pressure chamber to the second partial piston. This ensures that the compressed fuel cannot flow back into the closed pressure chamber. At the end of the injection, the return chamber 127 is disconnected from the line 44 and connected to the high pressure fuel source 2 through the control valve 8 so that a rail pressure is formed in the return chamber, and the pressure in the high pressure chamber is converted into a rail pressure. Descends. The closing piston is hydraulically compensated and closed by the force of the closing chamber spring 131 so that the injection ends. According to the pressure balance, the pressure intensifying piston 121 is returned to the initial position by the return spring 125, and the high pressure chamber 128 is charged from the closing pressure chamber 112 through the check valve 129, and the closing pressure The chamber is again supplied with fuel from the chamber 126.

In order to stabilize this switching process, structural measures are additionally provided for the damping of vibrations occurring between the high-pressure fuel source and the injector in some cases. In addition or alternatively to a suitable configuration of the throttle 3, a throttle check valve can be mounted at any position of the supply lines 4, 42, 45. In addition, the pressure enhancing piston, the closing piston and the valve hollow piston ensure, on the one hand, that fuel supply to the injection opening is ensured, and on the other hand the fuel pressure is effective in axial force against the closed piston in the high pressure chamber region. It is important to have a working surface to perform. The force is directed to the pressure intensifying piston, ie the force acts in the open direction.

4 shows another configuration of an injector with an integrated pressure intensifier. With the structure according to FIG. 3, the closed piston 113 is guided hydraulically until it is leaking lost through the second partial piston 123. Thus, instead of the valve hollow piston 206 of FIG. 3 being removed, a separate check valve 215 is provided for filling the high pressure chamber 128 connected to the return chamber 127 in the illustrated embodiment. Likewise, in the structure according to FIGS. 1 and 3, the chamber 126 and the closed pressure chamber 112 can always be exchanged with fuel, and the spring 127 for returning the pressure booster is not the chamber 126 but the return chamber. It differs from the structure according to FIG. 3 in that it is located within 127. The spring is tensioned between the stepped taper of the injector housing and the first partial piston 122. The limiting element 218 fixed to the injector housing limits the freedom of movement of the pressure intensifying piston so that the chamber 126 always contains various volumes from zero.

In alternative embodiments, the check valve 215 may be directly connected with the chamber 126 or line 4, instead of the return chamber 127. The check valve may be integrated into the pressure intensifying piston 121 or the closing piston 113.

In the entire embodiment, the closed pressure chamber 12 or 112 and the chamber 26 or 126 are embodied by a common closed pressure working chamber 12, 26, 47 or 112, 126, 130. All partial regions 12, 26 or 112, 126 are permanently connected for fuel exchange, for example via at least one fuel line 47 or at least one bore 130 integrated into the pressure intensifying piston. do. The pressure chamber 17 and the high pressure chamber 28 also consist of a common injection chamber 17, 28, 40, where the common partial regions of the injection chamber are permanently connected to one another for fuel exchange. The pressure chamber 17 and the high pressure chamber 28 may be connected to each other via the fuel line 40 (compare FIG. 1), or the pressure chamber may itself be configured by the high pressure chamber 128 (FIG. 3 and 4 compare).

FIG. 5 shows the time course of fuel pressure p in the high pressure chambers 28, 128. Curve 310 shows the pressure ratio during fast actuation of the 3/2 way piezo valve according to Fig. 2, and curve 311 shows slow valve actuation. The first position of the valve where the valve body is pressed against the first valve seat 53 is indicated by the stop position, and the second position of the valve where the valve body is pressed against the second valve seat 54 is indicated by the end position. do. In rapid valve operation, the valve body is electrically controlled so that the valve body quickly reaches the end position from the stop position, and in slow valve operation, the voltage applied to the piezo actuator is increased slowly so that the valve body shuts down from the initial position at a low speed. Is reached by location. Curves 320 and 321 show the pressure change in the return chamber of the pressure booster over time t. The formed stroke h of the piezo actuator, ie the stroke of the valve body movement, is shown by curves 330 and 331. The variable represents the pressure of the high pressure fuel source and the pressure in the high pressure rail of the common rail system, the variable pmax represents the maximum achievable high pressure fuel in the high pressure chamber, and the variable hmax represents the maximum stroke of the valve body. Indicates.

In the stop position of the valve body, the pressure booster is deactivated and the piston of the pressure booster returns to the initial position so that no injection is performed. Within the high pressure chamber and the return chamber there is a rail pressure (see time curves 31, 311, 320, 321 from zero to time point t1). At the end position hmax of the valve body, the pressure booster is fully activated and the pressure in the return chamber reaches a maximum value pmax. The closing piston is raised to perform injection. In the switching area between the stop position and the end position, the pressure booster is partially activated so that the pressure in the return chamber decreases with increasing stroke of the piezo valve, and the pressure-increasing piston increases the intermediate injection pressure which increases with increasing valve stroke. By forming, the injection proceeds at increased pressure. For simplicity of the drawing in the graph shown in FIG. 5, the nozzle opening pressure is only slightly different. In the slow operation of the valve, the pressure in the return chamber is continuously reduced to a small value from the time point t1, curve 331 to the time point t2 (curve 321), while the pressure in the high pressure chamber is gradually increased to the value pmax. (Curve 311). When the nozzle opening pressure is reached immediately after the time point t1, the closing piston is raised from the injection opening and fully opened, whereby the increased amount of fuel is injected by the increased pressure. At the time point t2, the maximum opening stroke hmax and the maximum injection pressure pmax of the valve body are reached. The closing process is carried out quickly at time t3 (to ensure rapid release of pressure at the end of the injection) (in English terminology for this, "rapid spill" is used.) The point at which the extended piezo actuator returns. At t3, the pressure in the high pressure chamber and the pressure in the return chamber are returned to the rail pressure, and the closing piston closes the injection opening again, At time t1, if the valve is quickly controlled (curve 330), the switching area is Passed quickly, the pressure in the high pressure chamber rapidly increases to the maximum level pmax before the time point t2 (curve 310), while at the same time the pressure in the high pressure chamber rapidly decreases to a small value (curve 320). In order to ensure rapid pressure release at the end of the injection, the closing process is preferably carried out quickly in a manner similar to that described above.

FIG. 6 shows the pressure ratio for the case where the piezo valve according to FIG. 2 is operated as a 3 / 3-way valve, for example. In this case, the valve body has, in addition to the stop position and the end attract, an intermediate position in which the valve body can stay for at least a predetermined time and the line 42 can be connected with the line 45 and the line 44. During that time a pressure balance is set in the return chamber at an intermediate pressure level PZ1, which pressure balance is determined together through the mass flowing into the low pressure system and flowing from the high pressure fuel source. Curve 410 represents the pressure progression in the high pressure chamber, and curve 420 represents the pressure progression in the return chamber. The h (t) graph shown below is the temporal progression of the closed piston stroke, and the third graph represents the temporal progression of the piezostroke H, ie the movement of the valve body. Hmax represents the maximum value for the piezostroke. The end position of the valve body in which the return chamber can be connected with the low pressure system can be set by the maximum value. The opening pressure Poe in the high pressure chamber is the pressure necessary for raising the closing piston. The time points t1 to t5 represent various time points following each other in an injection cycle comprising an initial injection, ie a first injection step for a low pressure level and a second injection step for a high pressure level.

At the time t1, the valve body is guided to the intermediate position through the corresponding control of the piezo actuator and held at this position until the time t3 (see H (t) -graph). The pressure in the return chamber drops to the intermediate pressure level PZ1, but the pressure in the high pressure chamber gradually rises. As soon as the pressure in the high pressure chamber raises the opening pressure at time t2, the injector is opened (see h (t) -diagram), and the pressure level is reached between the rail pressure level and the maximum pressure value achievable by the pressure booster. An initial spraying step is performed. At the time point t3, the piezo valve is guided to an end position (second position) having a stroke value Hmax, whereby the pressure in the high pressure chamber is lowered to a value close to zero, but the injection opening is kept wide open. The pressure in the high pressure chamber is then raised to the value pmax. This main injection continues until a time point t4 at which the valve returns to its initial position (H = 0), whereby pressure equalization to rail pressure is performed in the high pressure chamber and the return chamber, and after a while the closing piston at time point t5. Closes the injection opening (h = 0).

Optionally, the intermediate position can also be used for injection with a low injection pressure, where the intermediate position can be returned to the original position. This can be done, for example, at a small injection amount required in preliminary injection or idling.

In all embodiments, the closed pressure chamber 12 or 112 and the chamber 26 or 126 are implemented by a common working chamber 12, 47, 26 or 112, 130, 126, wherein all partial regions of the working chamber are For the exchange of fuel, for example, it is permanently connected to one another via at least one fuel line 47 or via at least one bore 130 integrated into the pressure intensifying piston. In addition, the pressure chamber 17 and the high pressure chamber 28 are formed by a common injection chamber 17, 28, 40, and all partial regions of the injection chamber are permanently connected to each other for fuel exchange. The pressure chamber 17 and the high pressure chamber 28 may be connected to each other via the fuel line 40 (compare FIG. 1), or the pressure chamber may itself be configured through the high pressure chamber 128 (FIG. 3). And comparison with FIG. 4).

FIG. 7 shows a variant of the embodiment according to FIG. 1 and is of the same configuration except that the throttle 520 is additionally mounted in the line 49, so that the high pressure chamber 28 and the closed pressure chamber 12 or the chamber ( The connection between 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 indicated by reference numeral 510 and hereinafter as the valve cross section.

Further determination for needle closure is achieved through appropriate determination of the flow cross section of the filling path 49 through proper selection of the flow cross section of the throttle 520 and the valve cross section 510 connecting the return chamber 27 to the pressure supply. Pressure can be established. In addition, the fill path 49 through the throttle 520 is very small, but is sufficient to fill the high pressure chamber 28 and return the pressure intensifying piston to the next injection position. In addition, the valve cross section 510 is sufficiently large so that the pressure in the return chamber 27 is rapidly formed as a rail pressure, and the pressure may be raised in the high pressure chamber according to the line configuration. As the pressure is rapidly formed in the high pressure chamber, a rapid pressure release to the rail pressure is formed by the pressure drop below the rail pressure in the high pressure chamber 28. Through the throttle 520, too fast pressure balance between the chamber 28 and the chamber 12 or 26 is prevented. Since the rail pressure continuously rises in the closing pressure chamber 12 in this step, a closing hydraulic force against the nozzle needle is formed.

In another alternative embodiment, the configuration of the flow cross section of the filling path 49 is ensured via a check valve 29 comprising a corresponding flow cross section, instead of through the use of a throttle.

FIG. 8 schematically shows the pressure progression achieved by the structure according to FIG. 7. The temporal passage of fuel pressure in the high pressure chamber 28 is indicated by reference numeral 1310, and the temporal passage of fuel pressure in the return chamber 27 of the pressure booster is denoted by reference numeral 1320.

The injection end is described below. After deactivation of the valve 8, pressure formation to the rail pressure is performed in the return chamber 27 and the closing pressure chamber 12, and at the same time, the rail pressure is stored in the high pressure chamber 28 and the pressure chamber 17. A rapid pressure drop of is performed. The latter pressure drop is carried out quickly so that the pressure in the high pressure chamber and the pressure chamber falls below the rail pressure. By precisely performing the needle closing at this stage, additional hydraulic force is generated to the nozzle needle, so that a quick needle closing is achieved and the fuel amount can be supplied into the combustion chamber of the engine more accurately. In another process, the rail pressure in the high pressure chamber and the pressure chamber is adjusted. Excess above the rail pressure shown at run 1320 is hydraulically limited and can be minimized or suppressed by appropriate line configuration. Rapid pressure build up in the return chamber is important for continued rapid pressure drop below the rail pressure in the high pressure chamber.

Claims (16)

A pressure intensifier comprising a movable pressure intensifier piston is connected between the fuel injector and the high pressure fuel source, the pressure intensifier piston separates the chamber connectable to the high pressure fuel source from the high pressure chamber connected with the fuel injector, and the return of the pressure intensifier is returned. The fuel pressure in the high pressure chamber can be changed through fuel charging and returning of the chamber, and the fuel injector can be supplied from a high pressure fuel source, including a movable closing piston for opening and closing the injection opening. A fuel injector having a fuel injector, By closing the closing piston 13; 113 into the closing pressure chamber 12; 112, the closing piston can be pressurized by fuel pressure to create a force acting on the closing piston in the closing direction, the closing pressure chamber ( 12; 112 and chambers 26; 126 are configured through a common working chamber, and all partial regions 12, 47, 26; 112, 130, 126 of the working chamber are permanently connected to each other for fuel exchange ( 47; 130). The pressure enhancing piston of claim 1, wherein the pressure enhancing piston is disposed coaxially with respect to the closed piston, and the partial region 112 of the operating chamber supported by the closed piston is connected to the other portion of the operating chamber through a bore 130 integrated into the pressure enhancing piston. Fuel injection device, characterized in that connected to. 3. The fuel injection device according to claim 2, wherein the end opposite to the injection opening of the closing piston is hydraulically sealed through the bore (130) until there is a leakage loss. Fuel injection according to any one of the preceding claims, characterized in that the fuel injector comprises a pressure chamber (17; 205, 128) for supplying fuel to the injection opening and for applying the closing piston with a force acting in the open direction. Device. 5. The pressure chamber (17; 205, 128) and the high pressure chamber (28; 128) comprise a common injection chamber (17, 28, 40; 205; 128), and all partial regions of the injection chamber (5). 17, 28; 205, 128 are connected permanently to each other for fuel exchange. Fuel injection device according to claim 5, characterized in that the pressure chamber (17) and the high pressure chamber (28) are connected to each other via a fuel line (40). 6. A fuel injection device according to claim 5, wherein the pressure chamber consists of a high pressure chamber (128). Fuel injection device according to any of the preceding claims, characterized in that the closed pressure chamber (112) and the return chamber (127) are supported by each other via a partial piston (123) of the pressure intensifying piston (121). Fuel injection device according to any of the preceding claims, characterized in that the high pressure chamber (28; 128) is connected with the closed pressure chamber (12; 112) via a check valve (29; 129). 10. The fuel injector of claim 9, wherein the high pressure chamber and the closed pressure chamber are throttled such that the pressure in the high pressure chamber can be below the pressure of the high pressure fuel source during the closing process. 9. The fuel injector according to claim 1, wherein the high pressure chamber is connected with the return chamber via a check valve. Fuel injection device according to any of the preceding claims, characterized in that the return chamber (27; 127) can be selectively connected with a low pressure line (44) or a high pressure fuel source (2) via a valve (8). 13. The valve of claim 12, wherein the valve is a piezo valve having first and second positions, the piezo valve connecting the return chamber to the high pressure fuel source at the first position and to the low pressure line 44 at the second position. A fuel injector characterized in that. 14. The fuel injection device according to claim 13, wherein the piezo valve is configured such that a switching speed between the first position and the second position can be changed. The fuel injection device according to any one of claims 12 to 14, wherein the valve is guideable to at least one intermediate position such that an intermediate pressure level is formed in the return chamber. 16. The fuel injector of claim 15, wherein the valve connects the return chamber to the high pressure fuel source and the low pressure line in an intermediate position.