EP1613856B1 - Fuel injector provided with a pressure transmitter controlled by a servo valve - Google Patents

Abstract

The invention relates to a fuel injector for injecting a fuel into the combustion chamber (23) of an internal combustion engine. The inventive injector (18) comprises a pressure transmitter (3) whose pressure relay piston (4) separates the working chamber (5) continuously receiving the fuel supplied by a pressure source (1,2) from a differential decompression pressure chamber (6). A pressure fluctuation is produced in said differential pressure chamber (6) by means of a servo valve (24) which closes or opens a hydraulic connection (21, 39, 42) between the differential pressure chamber (6) and a first return run (28) on a low-pressure side. The servo valve (24) comprises a piston (32) arranged between a control chamber (36) and first hydraulic chamber (38). A hydraulic surface (44) which continuously brings the piston (32) in the open position thereof when the pressure system is actuated, and a sealing surface (40) which closes or opens a return run (28) on a low pressure side are formed on said piston.

Description

For introducing fuel into direct-injection internal combustion engines, stroke-controlled injection systems with high-pressure storage space (common rail) are used. The advantage of these injection systems is that the injection pressure can be adapted to load and speed in a wide range. To reduce emissions and achieve high specific power, high injection pressure is required. The achievable pressure level of high-pressure fuel pumps is limited for reasons of strength, so that pressure amplifiers in the fuel injectors are used to further increase the pressure in fuel injection systems.

State of the art

Out DE 102 18 904 A1 a fuel injection device for internal combustion engines with a fuel injector with a pressure booster for increasing the injection pressure is known. The pressure booster has a pressure booster piston which is exposed to respective pressure surfaces of a working space, a differential pressure chamber and a compression space. The pressure intensifier and an injection valve member are driven by a servo valve comprising a switching element and a servo valve piston. The servo valve piston acts on a valve member which, with a first sealing seat, separates a first hydraulic space under system pressure from a second hydraulic chamber connected to low pressure and connected to the return system. The first hydraulic space is also connected via a control line to the differential space. By actuating the actuating element, an opening force is exerted on the valve member via the valve piston, which opens the first valve seat and closes the second valve seat, which is assigned to a connection to the system pressure. This is the result Control line, which leads into the differential pressure chamber of the pressure booster, connected via the opened first sealing seat with the low pressure side, so that the differential pressure chamber is disconnected from the system pressure. The system pressure acting on the working space presses the pressure booster piston into the compression space, whereby fuel is compressed there and passed through a high-pressure line into a nozzle needle pressure chamber, thereby lifting the nozzle needle from the nozzle needle seat and injecting the fuel with the injection pressure boosted by the system pressure.

DE 101 23 914 has the subject of a fuel injection device for internal combustion engines with a fuel injector which can be supplied by a high-pressure fuel source. Between the fuel injector and the high-pressure fuel source is connected to a movable pressure booster piston having pressure booster. The pressure booster piston separates a connectable to the high-pressure fuel source space from a high-pressure chamber connected to the fuel injector. By filling a rear space of the pressure booster device with fuel or by emptying the rear space of fuel, the fuel pressure in the high-pressure chamber can be varied. The fuel injector has a movable closing piston for opening and closing injection openings. The closing piston protrudes into a closing pressure chamber, so that the closing piston can be acted upon by fuel pressure in order to achieve a force acting on the closing piston in the closing direction. The closing pressure chamber and the rear space are formed by a common closing pressure-return chamber, wherein all portions of the closing pressure-return space are permanently interconnected to exchange fuel. There is provided a pressure space for supplying the injection openings with fuel and for acting on the closing piston with a force acting in the opening direction. A high-pressure chamber communicates with the high-pressure fuel source in such a way that, apart from pressure oscillations, at least the fuel pressure of the high-pressure fuel source can constantly be present in the high-pressure chamber, the pressure chamber and the high-pressure chamber passing through a common injection space be formed. All sections of the injection space are permanently connected to each other for the exchange of fuel.

DE 102 294 15.1 refers to a device for Nadelhubdämpfung pressure-controlled fuel injectors. Disclosed is a device for injecting fuel into a combustion chamber of an internal combustion engine, which comprises a fuel injector which can be acted upon by a high-pressure source with high-pressure fuel. The fuel injector is actuated via a metering valve, wherein an injection valve member is enclosed by a pressure chamber and the injection valve member can be acted upon in the closing direction by a closing force. The injection valve member is associated with a independently movable damping element, which limits a damping chamber and at least one overflow channel for connecting the damping chamber having a further hydraulic space. According to DE 102 294 15.1 the control of the fuel injector with a 3/2-way valve, which may represent a cost effective and space-saving injector, but this valve has a relatively large return flow rate of the pressure booster has to control.

In place of the DE 102 294 15.1 known embodiment of a 3/2 valve and servo valves can be used, which are formed leak-free in the idle state of the servo valve on the guide portion, which affects the efficiency of a fuel injector low. The disadvantage, however, is the fact that in the open state of the servo valve piston of the 3/2-way valve, no pressure surface pointing in its opening direction is subjected to system pressure. This makes the movement of the servo valve piston in its housing very sensitive to tolerances. Furthermore, a slow opening speed of the servo valve piston can not be achieved, whereby the small quantity capability of a servo valve configured in this way is limited. In the open state of the servo valve piston, only an insufficient closing force arises at a second valve seat formed on it, which can lead to leaks and increased wear.

Presentation of the invention

In order to achieve a defined movement of a servo valve piston of a servo valve for actuating a fuel injector, a servo valve designed as a 3/2-way valve is proposed which has a hydraulically effective surface which can be acted upon in the opening direction and which is constantly subjected to system pressure. The system pressure corresponds to the pressure level prevailing in the high-pressure reservoir. By this measure, the movement of the servo valve piston can be easily by the vote of inlet and outlet throttle on servo valve. By a slowly proceeding opening movement of the servo valve piston, a good representability of small pilot injection quantities and a vibration-free pressure build-up can be ensured. Due to the defined opening force, the servo valve proposed according to the invention becomes insensitive to tolerance to frictional influences, so that manufacturing-related tolerance scattering and the associated large scatter of injection quantities can be avoided.

Furthermore, the invention proposed, designed as a 3/2-way valve servo valve in the idle state does not occur on a guide portion leakage currents. This means a significant improvement in injector efficiency; due to the small guide lengths possible thereby on the servo valve piston, a small structural length of the servo valve can be made possible, which favorably influences the overall height of a fuel injector with pressure booster in an injector body comprising the servo valve, i. The space requirement of such a trained fuel injector is considerably reduced.

If a sealing seat formed on the servo valve piston of the servo valve is formed as a flat seat, the housing of the servo valve can advantageously be designed as a multi-part housing, whereby an axial offset of components relative to one another can be compensated. This compensation possibility production-related component tolerances and the good accessibility for the production of the sealing seat ensures a simple and cost manufacturability of the invention proposed servo valve.

drawing

• Es zeigt:

  Figur 1

  eine erste Ausführungsvariante eines als 3/2-Wege-Ventil ausgebildeten Servoventiles mit führungsleckagefreiem Servoventilkolben,

  Figur 2

  eine weitere Ausführungsvariante eines Servoventilkolbens eines 3/2-Servoventiles mit einem als Kegel-Dichtsitz ausgebildeten ersten Sitz und einem als Schieberdichtung ausgebildeten weiteren Sitz,

  Figur 3

  eine Ausführungsvariante eines 3/2-Servoventiles mit einem Servoventilkolben, an dem eine Steuerhülse aufgenommen ist und

  Figur 4

  eine Ausführungsvariante eines 3/2-Servoventiles mit gestrecktem Servoventilkolben.

With reference to the drawing, the invention will be described in more detail below:

• It shows:

  FIG. 1

  a first embodiment of a trained as a 3/2-way valve servo valve with guide leak-free servo valve piston,

  FIG. 2

  2 shows a further embodiment variant of a servo valve piston of a 3/2 servo valve with a first seat designed as a conical sealing seat and a further seat constructed as a slide seal,

  FIG. 3

  a variant of a 3/2-servo valve with a servo valve piston to which a control sleeve is received and

  FIG. 4

  a variant of a 3/2-Servoventiles with stretched servo valve piston.

variants

FIG. 1 is a first embodiment of an inventively proposed 3/2-servo valve for controlling a fuel injector containing a pressure booster refer.

A working space 5 of a pressure booster 3 is acted upon by high-pressure fuel via a pressure source 1 and a high-pressure feed line 2 adjoining it. The working space 5 is permanently acted upon by the high pressure fuel of the pressure source 1. The pressure booster 3 comprises an integrally formed booster piston 4, which separates the working space 5 from a differential pressure chamber 6 (back space). The booster piston 4 is acted upon by a return spring 8, which is supported on the one hand on a recessed in an injector body 19 support disk 7 and on the other hand on a mounted on a pin of the booster piston 4 stop disc. The pressure booster 3 further comprises a compression chamber 9 which communicates via an overflow line 10 with a control chamber 12 for an injection valve member 14 in connection. In the overflow line 10 from the differential pressure chamber 6 (back space) to the control chamber 12 for the injection valve member 14, a first throttle body 11 is added.

In the control chamber 12 for the injection valve member 14, a spring element 13 is received, which acts on an end face of the needle-shaped injection valve member 14. The injection valve member 14 includes a pressure stage which is enclosed by a pressure chamber 16. The pressure chamber 16 is acted upon by a pressure chamber inlet 17, which branches off from the compression chamber 9 of the pressure booster 3, with fuel under pressure translated. From the differential pressure chamber 6 of the pressure booster 3, a discharge line 21 extends into the first housing part 26 of the servo valve housing 25. The compression space 9 of the pressure booster 3 acting end face of the booster piston 4 is identified by reference numeral 20. Due to the pressure level at the injection valve member 14, this causes an opening movement when the pressure chamber 16 is pressurized, so that injection openings 22 flow from the pressure chamber 16 along an annular gap and into a combustion chamber 23 of a self-igniting internal combustion engine.

The injection chamber 14 acting on the control chamber 12 is connected via a second throttle point 15 to the compression chamber 9 of the pressure booster 3 in hydraulic communication.

Above the injector body 19 of a fuel injector 18, a servo valve housing 25 is arranged, which receives a servo valve 24. In the FIG. 1 illustrated embodiment, the servo valve housing 25 is formed in two parts and includes a first housing part 26 and a second housing part 27. The two-part design of the servo valve housing 25 according to the in FIG. 1 illustrated embodiment, allows good accessibility for processing of the sealing seat and a slide edge, resulting in a simple and cost manufacturability of the servo valve 24 results.

From the high-pressure feed line 2, via which the working space 5 of the pressure booster 3 is acted upon by high-pressure fuel, a supply line 29 branches off into the valve housing 25. The supply line 29 opens into a first hydraulic chamber 38 of the first housing part 26 of the servo valve housing 25. The first hydraulic chamber 38 encloses a servo valve piston 32, which comprises a passage 33. In the passage 33 of the servo valve piston 32, a third throttle body 34 is formed. Through the passage 33, fuel flows from the first hydraulic chamber 38 into a control chamber 36 of the servo valve 24. A pressure relief of the control chamber 36 takes place upon actuation of a switching valve 30, at its opening control volume from the control chamber 36 via a flow restrictor 37 (fourth throttle) containing return is connected to a further low-pressure side return 31 and fuel is derivable in these. The control chamber 36 of the servo valve 24 is limited by an end face 35 at the top of the servo valve piston 32. This is located at the head of the servo valve piston 32 an effective in the opening direction of the servo valve piston 32 annular surface, which is acted upon by the pressure prevailing in the first hydraulic chamber 38, opposite. In addition, a first sealing seat 40 in a second hydraulic chamber 39 and a control edge 41 are formed on the servo valve piston 32. About the first sealing seat 40, the connection to a drain control chamber 42, from which a low-pressure side return line 28 branches, released or closed. By means of the control edge 41, which in the in FIG. 1 illustrated variant of the servo valve 24 is formed as a slide sealing edge 43, the pressurized under system pressure first hydraulic chamber 38 is sealed in a vertically moving servo valve piston 32 against the second hydraulic chamber 39. The two returns 28, 31 on the low pressure side are combined as possible to a return, which opens into a fuel tank.

In support of the movement of the servo valve piston 32 in the first housing part 26 may - although in FIG. 1 not shown - spring forces are applied via springs on the servo valve piston 32. In the FIG. 1 shown first embodiment of the servo valve 24 allows an extremely compact design of the servo valve 24. The first sealing seat 40 of the servo valve 24 is shown in the illustration FIG. 1 formed as a flat seat, but could also be used as a conical seat (see FIG. 2 ) Ball seat or as a slide edge are formed. Advantageously, can be used by the formation of the first sealing seat 40 as a flat seat a multi-part valve body 25. By means of the formed as a flat seat first sealing seat 40 can be compensated for any production due axis offsets easily. Furthermore, a very high surface pressure and thus a good seal is achieved by the applied in the control chamber 36 of the servo valve 24 closing force on the flat seat of the first sealing seat 40. The first sealing seat 40 can be designed either as a sealing edge or as a sealing surface. The sealing force can be adjusted via the pressure surface with respect to the flow control chamber 42. As a result, when using a sealing surface, an optimal design of the surface pressure is possible, which on the one hand both a sufficient tightness and on the other hand also a lesser wear can be realized.

FIG. 2 shows a further embodiment of the present invention proposed servo valve, wherein the first sealing seat is designed as a conical seat.

The representation after FIG. 2 is also a fuel injector 18 can be seen, which contains a pressure booster 3. The working space 5 of the pressure booster 3 is supplied via a pressure source 1 (common rail) via high-pressure line 2 with high-pressure fuel. In contrast to the embodiment of the pressure booster 3 according to the embodiment according to FIG. 1 is the booster piston 4 of the pressure booster 3 according to the illustrations in FIG. 2 formed in several parts. In the injector body 19 of the fuel injector 18, a support plate 7 is inserted, which constitutes an upper abutment surface for the upper part of the multi-part booster piston 4. The lower part of the booster piston 4 is acted upon by a return spring 8 which is supported on the housing side; the compression space 9 of the pressure booster 3 is limited over the end face 20 of the lower part of the booster piston 4. From the differential pressure chamber 6 (back space) of the pressure booster 3, a first throttle point 11 containing overflow line 10 branches off. The overflow line 10 connects the differential pressure chamber 6 (back space) of the pressure booster 3 to the control chamber 12 for controlling the lifting movement of the needle-shaped injection valve member 14. From the compression chamber 9 of the pressure booster 3 runs the pressure chamber inlet 17, which opens into the pressure chamber 16 surrounding the injection valve member 14. The injection valve member 14 includes a pressure stage having a hydraulically effective area. At this attacks the im Pressure chamber 16 pending fuel pressure and opens the injection valve member 14 so that fuel is injected via released when opening the injection valve member 14 injection openings 22, which open into the combustion chamber 23 of the self-igniting internal combustion engine.

Unlike in FIG. 1 illustrated embodiment, a damping piston 51 is added to the control chamber 12 for the injection valve member 14. The damping piston 51 is traversed by a vertically extending channel 53. The channel 53 is hydraulically connected via a fifth throttle point 52 in the conversion of the damping piston 51 with the control chamber 12. A formed on the damping piston 51 annular surface 55 is acted upon by a housing side supporting spring element 54. From the control chamber 12 for the injection valve member 14 extends a filling line 56 which contains a refill valve 50, which may be formed as a check valve to the compression chamber 9 of the pressure booster 3. About the refill 50 containing filling line 56 of the compression chamber 9 of the pressure booster 3 again with fuel filled.

The servo valve 24 according to the in FIG. 2 illustrated embodiment is added to the valve body 25. The servo valve 24 includes the control chamber 36, which is relieved of pressure via the switching valve 30 in the second low-pressure side return 31. Between the control chamber 36 and the switching valve 30, an outlet throttle 37 (fourth throttle point) is added. Opposite the control chamber 36 in the valve body 25 of the servo valve 24 is the first hydraulic chamber 38, which is separated by the control edge 41 from the second, here conically configured second hydraulic chamber 39. The second hydraulic chamber 39 is connected via the diversion line 21 to the differential pressure chamber 6 (back space) of the pressure booster 3. Also in the embodiment of the servo valve 24 according to FIG. 2 the control edge 41 is formed as a slider sealing edge 43. Unlike in FIG. 1 illustrated embodiment of the servo valve 24, the first sealing seat 40 of the servo valve piston 32 is formed as a conical seat. When the first sealing seat 40 is closed, the drain control space 42 formed below the servovalve piston 32 in the valve body 25 is sealed so that the first low-pressure-side return 28 is closed.

In a modification of the servo valve piston 32 as shown in FIG FIG. 1 , a pressurization of the control chamber 36 and the first hydraulic chamber 38 takes place in parallel via the supply line 29, which branches off from the working space 5 of the pressure booster 3. Consequently, the system pressure in the first hydraulic chamber 38, which is acted on via the second supply line section 58, is present via the supply line 29 as well as via a first supply line section 57, the third throttle point Containing 34, in the control chamber 36 of the servo valve 24 at. Due to the identity of the pressures in the first hydraulic chamber 38 and in the control chamber 36, a pilot leakage along the head of the servo valve piston 32 is excluded. The servo valve piston 32 is guided in the valve body 25 high pressure-tight. In the idle state is within the guide region of the head of the servo valve piston 32 on both sides, ie in the control chamber 36 and in the first hydraulic chamber 38 system pressure, so that no leakage current occurs on the low pressure side. The entire region of the servo piston 32, ie the control chamber 36, the first hydraulic chamber 38 and the second hydraulic chamber 39 and the control edge 41 is guided leak-free against the drain control chamber 42 and thus against the first low-pressure side via the first sealing seat 40 formed in the second hydraulic chamber 39 Return 28 sealed.

The basic mode of operation of the inventively proposed fuel injector, which is controlled via the servo valve 24, is based on the illustration in accordance with FIG. 1 described.

The working space 5 of the pressure booster 3 is constantly connected to the pressure source 1 and is constantly under the prevailing pressure level there. The compression chamber 9 of the push-type translator 3 is constantly connected via the pressure chamber inlet 17 to the pressure chamber 16 which surrounds the injection valve member 14. The pressure booster 3 further includes the differential pressure space 6 (back space) for controlling the pressure booster 3 either at system pressure, i. pressurized in the pressure source 1 prevailing pressure level or separated from this pressure in the low-pressure side return 28 is relieved of pressure. In the deactivated state of the differential pressure chamber 6 (back space) of the pressure booster 3 via the Absteuerleitung 21, the open control edge 41, the supply line 29 is connected to the pressure accumulator 1, so that the pressures in the working chamber 5 and the differential pressure chamber 6 (back space) of the pressure booster correspond to each other and the booster piston 4 is balanced and no pressure boost takes place.

To activate the pressure booster 3, a pressure relief of the differential pressure chamber 6 (back space). In order to bring about this pressure relief, the switching valve 30 is activated, ie opened and the control chamber 36 of the servo valve 24 in the low-pressure side return 31 via the outlet throttle 37 relieved of pressure. Due to the falling pressure in the control chamber 36, the servo valve piston 32 moves upward in the vertical direction, moved by the pressing force acting on the opening surface 44 in the first hydraulic space 38. As a result, the first sealing seat 40 is opened while the control edge 41 is closed, since the slide edge 43 covers the opposite housing edge of the valve body 25. By the design of the throttle body 34 in the passage 33 of the servo valve piston 32 and the outlet throttle 37 is the movement speed of the servo valve piston 32 at its opening movement freely adjustable. Due to the defined opening surface 44 on the underside of the head of the servo valve 24, the servo valve piston 32 is constantly in compression in the opening direction. This allows a precise movement of the servo valve piston 32 and thus a stable persistence of the same at the opening stop in the open state of the servo valve piston 32 bring about.

When located in its open position servo valve piston 32 is a decoupling of the differential pressure chamber 6 (back space) of the pressure booster 3 from the system pressure, i. of the prevailing pressure in the accumulator 1 pressure levels. When the control edge 41 is closed, a control quantity flows out of the differential pressure chamber 6 (back space) via the outlet line 21 into the second hydraulic chamber 39, via the opened first sealing seat 40 into the process control chamber 42. From this flows the fluid which has been diverted from the differential pressure chamber 6 (backspace) Fuel quantity in the low-pressure side return 28 from.

Due to the retraction movement of the end face 20 of the booster piston 4 in the compression chamber 9, in this an increase in pressure, so that via the pressure chamber inlet 17 corresponding to the transmission ratio of the pressure booster 3 under elevated pressure fuel to the pressure chamber 16, which surrounds the injection valve member 14, flows. Due to the pressure stage formed on the injection valve member 14 in the region of the pressure chamber 16, this opens against the action of the spring 13, so that the injection nozzles 22 are opened at the combustion chamber end of the fuel injector 18 and fuel can be injected into the combustion chamber 23 of the internal combustion engine. When fully open injection valve member 14, the second throttle body 15 is closed between the control chamber 12 and the compression chamber 9 of the pressure booster 3, so that sets no leakage during the injection process.

To terminate the injection process, a renewed actuation of the switching valve 30, this is moved to its closed position, so that builds up in the control chamber 36 via the passage 33, the first hydraulic chamber 38 and the opening into this supply line 29 of the pressure accumulator 1 prevailing system pressure. As a result of the pressure force built up in the control chamber 36, the servo valve piston 32 moves down into its starting position, the first sealing seat 40 being closed to the low-pressure side return 28 and the control edge 41 being opened. Since the end face 35 on which the pressure prevailing in the control chamber 36 acts is greater than the opening pressure surface 44 in the first hydraulic chamber 38, a defined and fast-running closing movement of the servo valve piston 32 is achieved in its closed position.

To support the lifting movement of the servo valve piston 32 and additional springs in the first housing part 26 could be arranged.

In the differential pressure chamber 6 (back space) of the booster and in the control chamber 12, via which the injection valve member 14 is controlled, now takes place a pressure build-up on the pressure prevailing in the pressure accumulator 1 pressure level via the supply line 29, which branches off from the high pressure supply line 2 of the high-pressure accumulator 1, the open control edge 41, the second hydraulic chamber 39 and the Absteuerleitung 21, which opens into the differential pressure chamber 6 (back space). From there, a pressure build-up takes place via the overflow line 10, which contains the first throttle point 11 into the control chamber 12.

At the same time takes place at pressure build-up in the differential pressure chamber 6 (back space) of the pressure booster refilling the compression chamber 9 via the branching off from the control chamber 12 for actuating the injection valve member 14 line in which the second throttle body 15 is formed.

The first sealing seat 40 can be used both as a flat seat, which allows a high surface pressure, and as a conical seat (comparisons according to FIG FIG. 2 ) are formed as a ball seat or as a slide edge. About the in FIG. 1 illustrated flat seat as the first sealing seat 40 can compensate for any production-related axial offset. About the pending in the control chamber 36 high pressure level, the generation of a sufficient closing force, so that at the first sealing seat 40 in its closed position, a high surface pressure arises and thus a good sealing effect is ensured.

With the in FIG. 2 illustrated embodiment using a damping piston 51 which acts on the injection valve member 14, a reduction in the opening speed of the needle-shaped injection valve member 14 can be achieved. The damping behavior of the damping piston 51 can be adjusted by the dimensioning of this acting spring element 54 and by the dimensioning of the formed in the wall of the damping piston 51 throttle element 52. According to the in FIG. 2 illustrated embodiment, the refilling of the compression chamber 9 of the pressure booster 3 does not take place via the second throttle point 15 as in the embodiment according to FIG. 1 but via a branching from the control chamber 12 of the injection valve member 14 filling line 56 in which a designed as a check valve refill valve 50 is added.

The inventively proposed 3/2-servo valve 24 can be used to control all pressure booster 3, which are controlled via a pressure change of their differential pressure chamber 6 (backspace).

FIG. 3 is a variant of a 3/2-Servovalve with a servo valve piston refer to which a control sleeve is added.

In the FIG. 3 illustrated embodiment of a fuel injector 18 with pressure booster 3 is acted upon by a high pressure source 1 via the high pressure supply line 2 with high pressure fuel. About the high pressure line 2, the working space 5 of the pressure booster 3 is filled with system pressure, in which a return spring 8 is added, which is supported on the one hand on a support plate 7 and on the other hand via a stop surface biases the booster piston 4, which separates the working chamber 5 from the differential pressure chamber 6. The end face 20 of the booster piston 4 limits the compression chamber 9, which is acted upon by the activation of the pressure booster 3 via the pressure chamber inlet 17 of the pressure chamber 16 with high pressure fuel.

In the FIG. 3 illustrated embodiment of the fuel injector 18 includes the control chamber 12, which is bounded by a control chamber sleeve 62. The control chamber sleeve 62 is biased by the spring 13, wherein the spring 13 is supported on a collar of the injection valve member 14. At injection valve member 14, feed surfaces 64 formed as polished portions are formed below the collar. Via these inflow surfaces 64, the fuel flows from the pressure chamber to injection openings 22, which open into the combustion chamber 23 of the self-igniting internal combustion engine. The control chamber 12 of the fuel injector 18 is acted upon on the one hand via a first throttle point 11, which branches off from the pressure chamber inlet 17 with fuel; the pressure relief of the control chamber 12 via the second throttle body 15 upon actuation of a switching valve 60. If the switching valve 60 is actuated, a Absteuermenge via the second throttle point 15 is derived in an injector 61 return.

The pressure booster 3 according to the in FIG. 3 illustrated embodiment is actuated via the servo valve 24. The servo valve 24 includes the valve piston 32 having a servo valve piston portion 65. The servo valve piston 32, 65 is controlled via the pressurization or pressure relief of the control chamber 36. On the pressure side, the control chamber 36 of the servo valve 24 is acted upon by the high-pressure fuel via the first supply line section 57, in which the throttle restriction 34 is accommodated. A pressure relief of the control chamber 36 of the servo valve 24 via an actuation of the switching valve 30. When actuated flows a Absteuervolumen from the pressure-relieved control chamber 36 of the servo valve 24 via the outlet throttle 37 (4th throttle point) in the low-pressure side provided return 31 from.

The servo valve 24 comprises a housing 25, which comprises a plurality of housing parts 26, 27.

The servo valve piston 32, 65 is enclosed by the first hydraulic chamber 38 and the second hydraulic chamber 39. The first hydraulic chamber 38 is acted upon by the supply line 29, which branches off from the high-pressure line 2, with high-pressure fuel. In the second hydraulic chamber 39 opens the Absteuerleitung 21, via which a pressure relief of the differential pressure chamber 6 (back space) of the pressure booster 3 takes place.

The servo valve piston 32 also includes the hydraulic surface 44, on which a force acting on the servo valve piston 32 in the open position pressure force upon pressure relief of the control chamber 36 of the servo valve 24 attacks. In servo valve piston section 65, first recesses 63 are formed, which have slide sealing edges 43. The slider sealing edges 43 of the first recesses 63 cooperate with a control edge 41 formed on the second housing part 27. On servo valve piston portion 65, a control sleeve 67 is received, which is biased by a control sleeve spring 68, which in turn is supported on the first housing part 26 of the servo valve housing 25. The control sleeve 67 has a sleeve recess 71. The first sealing seat 40 according to the in FIG. 3 illustrated embodiment is designed as a flat seat and seals the Absteuerraum 42 (low pressure space) against the low-pressure side return 28 from. The functioning of in FIG. 3 illustrated embodiment of the controlled via the servo valve 24 Kraftsoffinjektors 18 with pressure booster 3 is as follows:

In the initial state prevails in the control chamber 36 of the servo valve 24 system pressure, which is present in the control chamber 36 via the third throttle point 34 when the switching valve 30 is closed. By the pressing force within the pilot chamber 36 of the servo valve piston, which acts on the end face 35 of the servo valve piston 32 and which is greater than the opening pressure force applied to the servo valve piston 32 via the hydraulic opening-effective surface 44, the servo valve piston 32 becomes its lower position hazards. In this position, the control edge 41 and the slider sealing edge 43 on the servo valve piston portion 65 are open, whereas the slide seal 69 is closed at the servo valve piston portion 65. Further, the first sealing seat 40 is against the Absteuerraum 42 (low pressure space) in its closed position. Since the second hydraulic chamber 39 is sealed by the first sealing seat 40 with respect to the Absteuerraum 42 (low pressure space), created when the servo valve piston 32, 65 no leakage current in the low-pressure side return 28, thereby reducing requirements the guide leakage (guide length and clearance) of the control sleeve 67 accommodated on the servo valve piston portion 65 can be set.

The first sealing seat 40 can be designed in many ways. In addition to the in FIG. 3 illustrated embodiment of the first sealing seat 40 as a flat seat, this can according to the embodiments, in FIG. 2 is shown, also formed as a conical seat or ball seat. Particularly advantageous is the in FIG. 3 represented by a multipart valve body, such as housing parts 26, 27 and 66, a simple manufacture of the valve seat of the first sealing seat 40 can be achieved. By the in FIG. 3 flat seat shown is compensated for any axial misalignment of the valve body to each other. In the FIG. 3 illustrated embodiment also has a large closing pressure force exerted by the pending in the control chamber 36 fuel pressure on the first sealing seat 40, which adjusts to this a high surface pressure and thus an excellent sealing effect.

In the idle state of the servo valve 24 of the differential pressure chamber (back space) 6 of the pressure booster 3 is acted upon by the first recesses 63 on the servo valve piston 65, and the first hydraulic chamber 38 with system pressure and the pressure booster 3 remains due to the hydraulic connection between the second hydraulic chamber 39, the Absteuerleitung 21 connected to the differential pressure chamber. Due to the same pressure level in the differential pressure chamber 6 and the working space 5 of the pressure booster 3 is deactivated. Upon actuation of the switching valve 30, a pressure relief of the control chamber 36 of the servo valve 24, whereby the servo valve piston 32, 65 opens. Due to the opening force acting on the hydraulic surface 44 via the first hydraulic chamber 38, the servo valve piston 32 is opened exactly. When opening, first the first sealing seat 40 is opened and the slider sealing edge 43 is brought into register with the control edge 41. The control sleeve 67 is now employed by the hydraulic pressure force in the second hydraulic chamber 39 to the third housing part 66, whereby a high-pressure-tight connection is achieved. Only then is an opening of the slide seal 69, when the servo valve piston section 65, the sleeve recess 71 releases. As a result, no short-circuit leakage current flows from the first hydraulic chamber 38 into the return line. The differential pressure chamber 6 (back space) of the pressure booster 3 is now connected via the second hydraulic chamber 39, the slide seal 69, the first sealing seat 40 and the Absteuerraum 42 (low pressure space) with the low-pressure side return 28 and the pressure booster 3 thus activated.

If, however, the switching valve 30 is closed again, then the servo valve piston 32, 65 moves through the force acting in the closing direction hydraulic pressure force in the control chamber 36 in its starting position. The hydraulic closing force ensures a precisely defined closing movement over the entire area of the servo valve piston 32, 65. In addition, a spring force can be provided to assist the closing movement. When closing the servo valve piston 32, 65, the slide seal 69 is first closed. As a result, the differential pressure chamber 6 (back space) of the pressure booster 3 is decoupled from the low-pressure return line 28. Only after a further closing stroke and thus after a delay time ti, an opening of the control edges 41, 43, so that the pressure booster 3 is completely deactivated. Subsequently, the first sealing seat 40 is closed.

Due to the delay time t ₁ between the closing of the slide seal 69 and the opening of the control edges 41 and the slide sealing edge 43, a pressure cushion on the injection valve member 14 remains after the main injection for a short time, which can be used for a post-injection under high pressure. According to this switching sequence, an overlapping of the opening cross sections on the slide seal 69 and the control edges 41, 43 is avoided.

The representation according to FIG. 4 is a variant with stretched trained Servoventilkolben a servo valve to remove. Unlike in FIG. 3 illustrated embodiment of a fuel injector 18, which is controlled via a servo valve 24, the servo valve piston 32 has a stretched servo valve piston section 65. According to this embodiment, 65 second recesses 70 are formed on the the Absteuerraum 42 (low pressure space) facing the end of the Servoventilkolbenabschnittes 65. At the periphery of the servo valve piston portion 65, two or more recesses 70 may be formed. According to this embodiment, the slide seal 69 is integrated directly into the first housing part 26 of the servo valve housing 25. According to this embodiment, the servo valve piston section 65 in FIG FIG. 3 illustrated control sleeve 67 omitted.

The functioning of in FIG. 4 illustrated embodiment is identical to that in connection with FIG. 3 illustrated operation of this embodiment of the fuel injector 18th

As shown FIG. 4 is formed at the Absteuerraum 42 (low pressure space) facing end face of the Servoventilkolbenabschnittes 65 a flat seat.

In addition to the in Figures 1-4 illustrated embodiments with a first sealing seat 40 in the servo valve housing 25, the servo valve 24 may also be formed as a pure slide-valve slide. In this case, care must be taken for a sufficient overlap length at the slide seal 69 in order to keep the leakage flow in the idle state of the fuel injector 18 small. In addition to the above-described operation as a 3/2-way valve, the servo valve 24 may also be formed as a 4/2-way valve, in which the function of the check valve is integrated into the slide valve.

LIST OF REFERENCE NUMBERS

1

pressure source

2

High pressure supply line

3

Pressure intensifier

4

Booster piston

5

working space

6

Differential pressure chamber (backspace)

7

support disc

8th

Return spring

9

compression chamber

10

overflow

11

1. restriction

12

Control chamber for injection valve member

13

feather

14

Injection valve member

15

2. Throttling point

16

pressure chamber

17

Pressure chamber inlet

18

fuel injector

19

injector

20

Face pressure intensifier piston 4

21

diversion line

22

Injection port

23

combustion chamber

24

servo valve

25

Servo valve housing

26

1st housing part

27

2nd housing part

28

low-pressure side return

29

Supply line servo valve

30

switching valve

31

further low-pressure side return

32

Servo valve piston

33

Through channel

34

3. Throttling point

35

Control surface Servo valve piston

36

Control room Servovalve

37

Outlet throttle (4th throttle point)

38

1. hydraulic space

39

2. hydraulic space

40

first sealing seat

41

control edge

42

Absteuerraum (low-pressure room)

43rd

Slide sealing edge

44

Opening surface

50

Wiederbefüllventil

51

damping piston

52

5. Throttling point

53

channel

54

spring element

55

ring surface

56

filling line

57

1. supply line section

58

2. Supply line section

60

Injektorschaltventil

61

injector return

62

Control chamber sleeve

63

1. recesses

64

Inlet areas (polished section)

65

Servo valve piston section

66

3rd housing part

67

control sleeve

68

Control sleeve spring

69

slide seal

70

2. recesses

71

Control sleeve recess

Claims (16)

1. Fuel injector for injecting fuel into a combustion chamber (23) of an internal combustion engine, having a pressure booster (3), whose booster piston (4) separates a working space (5), which is acted on permanently with fuel by means of a pressure source (1, 2), from a differential pressure space (6) which can be relieved of pressure, with a pressure change in the differential pressure space (6) taking place by means of an actuation of a servo valve (24) which opens or closes off a hydraulic connection (21, 39, 42) of the differential pressure space (6) to a low-pressure-side return line (28), with the servo valve (24) having a servo valve piston (32, 65) which is guided between a control space (36) and a first hydraulic space (38), and with the servo valve piston (32) having a first sealing seat (40), which opens or closes off the low-pressure-side return line (28), and a control edge (41) which separates the first hydraulic space (38) from a second hydraulic space (39), characterized in that the control space (36) is delimited by an end face (35) of the servo valve piston (32, 65), which end face (35), on the head of the servo valve piston (32, 65), is situated opposite an effective annular face which forms an effective hydraulic face (44) which is acted on at all times in the opening direction of the servo valve piston (32, 65) by a system pressure.
2. Fuel injector according to Claim 1, characterized in that the control space (36) and the first hydraulic space (38) are acted on with system pressure by means of a supply line (29) which proceeds from the pressure accumulator (1).
3. Fuel injector according to Claim 2, characterized in that the control space (36) of the servo valve (24) is acted on with system pressure by means of a passage duct (33), which extends through the servo valve piston (32), from the first hydraulic space (38) into which the supply line (29) opens out.
4. Fuel injector according to Claim 3, characterized in that the passage duct (33) of the servo valve piston (32) contains an integrated throttle point (34).
5. Fuel injector according to Claim 2, characterized in that the control space (36) and the first hydraulic space (38) are acted on in parallel with system pressure, the control space (36) being acted on with system pressure by means of a second supply line section (58) which branches off from the supply line (29) and the first hydraulic space (38) being acted on with system pressure by means of a supply line section (58) which branches off from the supply line (29).
6. Fuel injector according to Claim 5, characterized in that the first supply line section (57) contains a first throttle point (34).
7. Fuel injector according to Claim 1, characterized in that the first sealing seat (40) is embodied as a flat seat or as a conical seat and closes off an outflow control space (42) which is arranged at the low-pressure side.
8. Fuel injector according to Claim 1, characterized in that the control edge (41) is embodied as a slide sealing edge (43).
9. Fuel injector according to Claim 1, characterized in that the differential pressure space (6) which can be relieved of pressure via the servo valve (24) into the low-pressure-side return line (28) is hydraulically coupled to a control space (12), which holds a damping piston (51), for an injection valve element (14), with the damping piston (51) comprising a throttle point (52) which defines the opening speed of the injection valve element (14), and with the control space (12) being connected, for the actuation of the injection valve element (14), via a filling line (56) either to the control space (12) or to one of the hydraulic spaces (5, 6, 9) of the pressure booster (3).
10. Fuel injector according to Claim 1, characterized in that the actuation of the servo valve (24) takes place by means of a switching valve (30) which connects the control space (36) to a return line (31).
11. Fuel injector according to Claim 1, characterized in that the servo valve piston (32) comprises a reduced-diameter servo piston section (65) on which is held a preloaded control sleeve (67).
12. Fuel injector according to Claim 1, characterized in that the control sleeve (67) forms a slide control edge (69) with the servo valve piston section (65).
13. Fuel injector according to Claim 12, characterized in that the slide control edge (69) controls the connection to the low-pressure-side return line (28).
14. Fuel injector according to Claim 11, characterized in that the servo valve piston section (65) of the servo valve piston (32) has first cutouts (63) which comprise a slide sealing edge (43) which interact with a control edge (41) which is formed on the servo valve housing.
15. Fuel injector according to Claim 11, characterized in that the control sleeve (67) is acted on by means of a spring element (68) which is supported against a housing part (26) of the servo valve housing (25).
16. Fuel injector according to Claim 11, characterized in that the servo valve piston section (65) of the servo valve piston (32) has first cutouts (63) between the first hydraulic space (38) and the second hydraulic space (39), and second cutouts (70) which form a slide seal (69).

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