EP1756415A1

EP1756415A1 - Fuel injector with variable actuator transmission

Info

Publication number: EP1756415A1
Application number: EP05726519A
Authority: EP
Inventors: Wolfgang Stoecklein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-06-08
Filing date: 2005-04-15
Publication date: 2007-02-28
Anticipated expiration: 2025-04-15
Also published as: EP1756415B1; WO2005121544A8; US7406951B2; DE102004027824A1; WO2005121544A1; US20070246019A1; JP2007505255A; CN1965162A

Abstract

The invention relates to a fuel injector (1) which is used to inject fuel into the combustion chamber of an internal combustion engine. The fuel injector (1) comprises an injection valve member (9) which can be actuated directly by means of a piezoactuator (8). Said injection valve member is introduced into a nozzle body (3) of the fuel injector (1) and can be adjusted by a spring element (15) in the closed position. A hydraulic transmission arrangement (12, 14) is provided between the piezoactuator (8) and the injection valve member (9) in order to adapt the force which is to be applied by the piezoactuator (8) to the opening force characteristic of the injection valve member (9).

Description

Fuel injector with variable actuator ratio

Technical field

Fuel injection systems, which comprise a number of fuel injectors, are used to supply combustion engines with fuel. High-pressure accumulator fuel injection systems are used today in self-igniting internal combustion engines. The fuel injectors, each of which can be supplied with fuel via a high-pressure fuel accumulator (common rail), are controlled via solenoid valves or via piezo actuators. In fuel injectors, the actuating element of which is designed as a piezo actuator, a needle-shaped injection valve element can be controlled directly by changing the electrical voltage at the piezo actuator. When the piezo actuator is energized, the piezo crystal stack is elongated, which disappears when the energization is withdrawn.

State of the art

In the case of fuel injectors which are actuated by a piezo actuator, the crystal stack of the piezo actuator is elongated when energized. Depending on the degree of current supply, the piezo crystal stack of the piezo actuator is lengthened by a different amount. When the current supply is withdrawn, however, the piezo crystal stack returns to its original length. It has been found that intermediate positions of an injection valve element, which can be designed as a nozzle needle, are only insufficiently stable due to energization of the piezo crystal stack of the piezo actuator with different current levels.

If a piezo actuator is used in a fuel injector with a directly actuated injection valve member, the required intermediate positions of the injection valve member between its fully open and its completely closed position can consequently only be held in an insufficiently stable manner, which results in a considerable scatter in the intermediate position of the injection valve member in the combustion chamber the amount of fuel injected can be accompanied by the self-igniting spreading machine. In order to open an injection valve member in fuel injectors with direct needle control via a piezo actuator, large forces must first be overcome. The injector-shaped injection valve member is usually pressed into its seat with system pressure, ie in the case of high-pressure accumulator injection systems with rail pressure. These forces can be in the range of several 100 N. In order to be able to provide a sufficient fuel flow through the fuel injector in the case of the fully open injection valve, a stroke of the injection valve member of several 100 μm, approximately in the order of magnitude between 200 and 300 μm, must be able to be realized. The size of the maximum opening force Fmax, which can be in the range of several 100 N, for example 400 N, and the maximum stroke of the injection valve member in the range between 200 and 300 μm essentially determine the size of the piezo actuator that directly actuates the fuel injector ,

The length-to-diameter ratio of the piezo actuator can be varied by implementing, for example, a hydraulic transmission; alone, the volume of the actuator is determined by the maximum opening force F _max to be overcome and the maximum stroke of the needle-shaped injection valve gHedes to be realized.

Presentation of the invention

By means of the solution proposed according to the invention, the force provided by the piezo actuator is applied to the opening force curve via a, for example, two-stage translation, i.e. adapted to the seat forces of the injection valve member. Due to the adaptation of the opening force curve proposed according to the invention, a large force is available for opening the injection valve member, which can be configured as a needle-needle, when the injection valve member is pressurized by system pressure, with which the injection valve member can be brought out of the sitting position. In order to subsequently bring about a complete opening of the needle-shaped injection valve member, the translation is switched over from a certain stroke of the piezo actuator.

The proposed multi-stage translation of the force provided by the piezo actuator according to the invention also advantageously enables a stable intermediate stroke stop of the injection valve member to be achieved. Intermediate strokes of the injection valve between a stop defining its closed position and its open position, ie maintaining a ballistic position of the injection valve member, are particularly critical for the realization of small KxaftstoffVoluiriina to be injected into the combustion chamber of the self-igniting internal combustion engine. to look at the table. The solution proposed according to the invention, a two-stage or multi-stage translation of the force made available by the piezo actuator, enables reliable intermediate stroke positions of the fuel injector member of the fuel injector to be approached and maintained in a stable manner.

drawing

The invention is described in more detail below with reference to the drawing.

It shows:

FIG. 1 shows a fuel injector with direct control of the injector valve and a booster piston coupled within a pre-stroke sleeve,

Detail X

(FIG. 1.1) shows one of the booster pistons according to FIG. With a connecting bore formed in it, on an enlarged scale,

(Figure 1.2) the combustion chamber-side seat of the injector valve in a schematic representation,

FIG. 2 shows a further sleeve encircling a pre-stroke sleeve as shown in FIG. 1 to compensate for radial assembly tolerances,

Figure 3 shows a variant with a modified support position of one of the two booster pistons and

FIG. 4 shows a comparison of the forces and strokes of the piezo actuator that can be achieved by the step transmission compared to an actuation system without step translation.

Ausfährungsvarianten

FIG. 1 shows a longitudinal section through a fuel injector proposed according to the invention with direct control of the injector valve and a variable transmission ratio of the stroke path of a piezo actuator. A fuel injector 1 comprises an injector body 2, which is also referred to as a holding body. The injector body 2 of the fuel injector 1 is connected via a clamping nut 4 to a nozzle body 3 on a screw connection 5. The injector body 2 comprises a high-pressure connection 6, via which a cavity 7 formed in the injector body 2 is subjected to system pressure, for example the fuel pressure level prevailing in a high-pressure accumulator (common rail). A nozzle space inlet 11 runs from the cavity 7 of the injector body 2 to a nozzle space 10 formed in the nozzle body 3, which surrounds a needle-shaped injection valve head 9. In the area of the nozzle chamber 10, which is also acted upon by system pressure, a pressure stage is formed on the injection valve gHed 9 which can be embodied in the form of a needle. Due to the system pressure prevailing in the nozzle chamber 10, the needle-shaped injection valve gHed 9 is acted upon in the opening direction.

A piezo actuator 8 is accommodated in the cavity 7 of the injector body 2. The piezo actuator 8 is shown only schematically in the illustration according to FIG. 1 and comprises a multiplicity of piezocrystals stacked on top of one another, which are elongated when the piezo actuator 8 is energized. As a result, the piezo actuator 8 expands in the vertical direction within the cavity 7 of the injector body 2 and thereby provides the forces required to actuate the injector 9. If, on the other hand, the energization of the piezo actuator 8 is interrupted, the individual piezo crystals arranged one above the other in the vertical direction assume their original length again - seen in the vertical direction - so that the piezo actuator 8 as a whole resumes its original length in the non-energized state.

It can be seen from the illustration in FIG. 1 that a pre-stroke sleeve 13 encloses both a first piston 12 (ÜA) and a second piston 14 (ÜB). The two facing end faces of the first piston 12 (ÜA) and the second piston 14 (ÜB) as well as the pre-stroke sleeve 13 surrounding the two pistons 12 and 14 delimit a hydraulic coupling space 23. The outer diameter of the pre-stroke sleeve is denoted by dy.

There is a disk-shaped stop on the first piston 12 (ÜA), which abuts the underside of the piezo actuator 8. The disc-shaped stop 18 acts on both an inner spring element 16 and an outer spring element 17, which can be designed, for example, as spiral springs. The inner spring element 16 is supported on an end face of the preliminary stroke sleeve 13, while the outer spring element 17 is supported on a surface of the injector body 2, which in turn encircles the preliminary stroke sleeve 13. Both the injector body 2 and the pre-stroke sleeve 13 lie with their end faces facing away from the piezo actuator 8 along a parting line on an upper flat surface of the nozzle body 3. The diameter of the first piston 12 (ÜA) is denoted by d _A.

A cavity is formed below the pre-stroke sleeve 13 in the nozzle body 3 of the fuel injector 1, as shown in FIG. The second piston 14 (ÜB) is received in this cavity, the tapered end of which protrudes into the pre-stroke sleeve 13 and lies opposite the end face of the first piston 12 (ÜA) in the coupling space 23. The second piston 14 ÜB) is acted upon by a further spring element 21, which is supported on the one hand on a collar of the second piston 14 (ÜB) and on the other hand on the lower end face of the pre-stroke sleeve 13 above the cavity in the nozzle body 3. The cavity and a control chamber 20 acting on a piston face 19 of the second piston 14 (ÜB) are hydraulically connected via a schematically indicated bore 22. In the illustration according to FIG. 1, the piston end face 19 bears on a flat face of the nozzle body 3 above the injection valve head 9.

The control chamber 20, in which a control chamber spring element 15 is accommodated, is located below the second piston 14 (ÜB). The control chamber spring element 15 bears on the one hand on the piston end face 19 of the second piston 14 (ÜB) and on the other hand is supported on an end face of the needle-shaped injection valve head 9. The diameter of the needle-shaped injector 9 above the nozzle space 10 is denoted by d _N.

The detail X (FIG. 1.1) shows the second piston 14 (ÜB) on an enlarged scale.

It can be seen from this illustration that the cavity in the upper region of the nozzle body 3 of the fuel injector 1 is hydraulically connected via a bore 22 to the control chamber 20 delimited by the piston face 19 of the second piston 14 (ÜB). Instead of the illustrated bore 22, the hydraulic connection could also take place via grooves or other types of recesses on the circumferential surface of the second piston 14 (ÜB). H _v denotes a defined distance between the lower end face of the preliminary stroke sleeve 13 and a collar on the second piston 14 (ÜB).

First, the needle-shaped injection valve gHed 9 is pressed into the nozzle seat via the control chamber spring element 15 and consequently closes the injection openings (not shown in FIGS. 1 and 1.1), via which fuel can be injected into the combustion chamber of the self-igniting internal combustion engine. The second piston 14 (ÜB) is received via the further spring element 21 - in the cavity of the nozzle - body 3 - pressed down against a plane surface formed in the nozzle body 3. The piston end face 19 of the second piston 14 (ÜB) bears against this. The spring force of the further spring element 21, received in the cavity of the nozzle body 3, exceeds the spring force of the control chamber spring element 15. At the same time, the pre-stroke sleeve 13 is pressed by the inner spring element 16 against the upper end face of the nozzle body 3. This position represents the starting position of the pre-stroke sleeve 13. In this state there is the distance designated h _{v in} FIGS. 1 and in detail X (FIG. 1.1) between the lower end face of the pre-stroke sleeve 13 and a collar 26 on the circumference of the second piston 14 ( OVR).

In this state it is assumed that the piezo actuator 8 is energized, i.e. whose piezo crystals are under tension and are therefore elongated in the vertical direction.

If the current supply to the piezo actuator 8 is reduced, the first piston 12 (ÜA) moves out of the hydraulic coupling space 23 due to the shrinking length of the piezo crystals of the piezo actuator 8. As a result, the pressure in the hydraulic coupling space 23 drops. The second piston 14 (ÜB) acts on the pressure change in the hydraulic coupling chamber 23 and moves synchronously with the piezo actuator 8. Due to the vertical movement of the second piston 14 (ÜB), the pressure in the control chamber 20 is reduced. The further the voltage at the piezo actuator 8 is reduced, the more the pressure in the control chamber 20 drops. If a critical pressure, ie an opening pressure pe _{> of} the needle-shaped injection valve head 9 is reached, this opens. The opening pressure, p _ö , from which the needle-shaped injection valve gHed 9 opens, is determined by the nozzle seat diameter d _s (see illustration according to FIG. 1.2), the system pressure p R and the diameter d _N , ie by the diameter of the needle-shaped injection valve gHedes 9 self-defined, according to the following relationship:

PÖ = PCR (d _N ² - d _s ² ) / d _N ² with

P _C R = system pressure d _N = injector diameter gHed 9 d _s = seat diameter

The spring forces acting on the needle-shaped injection valve gHed 9 have been neglected here for reasons of simplification. During the opening phase, the effective piston diameter with which the piezo actuator 8 generates a negative pressure in the control chamber 20 is the diameter d _A , ie the diameter of the first piston 12 (ÜA). This means that between the piezo actuator 8 and the needle-shaped injection valve gHed there is now a small transmission ratio (or a small reduction ratio depending on the choice of parameters) of

iι = d _A ² / d _N ²

prevails. During the opening of the needle-shaped injection valve head 9, this opens together with the vertically upward movement of the first piston 12 (ÜA) or the second piston 14 (ÜB). The opening force resulting from the pressure infiltration of the nozzle seat initially only acts on the piezo actuator 8 via the smaller piston diameter d _{A of} the first piston 12 (ÜA). Due to the pressure infiltration of the injector 9 in the region of the nozzle seat and the opening force that is established, the piezo actuator 8 can Check the movement of the needle-shaped injection valve handle 9. Only when the second piston 14 (ÜB) strikes with its collar 26 on the lower end face of the preliminary stroke sleeve 13 does the transmission ratio change to d _v = diameter of the pre-stroke sleeve 13 and d _N = diameter of the injector 9.

The second gear ratio i ₂ is larger than the first gear ratio ii. In order to open the injection valve gHed 9 in the form of a needle, the voltage at the piezo actuator 8 must first be lowered more, since the piezo actuator 8 pulls the pre-stroke sleeve 13, the diameter of which is denoted by d _v , out of the control chamber 20. In order to open the needle-shaped injection valve gHed 9 further, the voltage at the piezo actuator 8 is first reduced more, since the piezo actuator 8 pulls the pre-stroke sleeve 13 with the diameter dv out of the control chamber 20 and the pressure in the control chamber 20 is lower than the system pressure, ie rail pressure. To completely open the needle-shaped injection valve head 9, however, only a smaller stroke of the piezo actuator 8 is now necessary, since the transmission ratio i _{2 can} now be chosen to be large. If, on the other hand, only a small injection quantity is to be introduced into the combustion chamber of a self-igniting internal combustion engine, the needle-shaped injection valve member 9 will advantageously remain at the pre-stroke stop until the voltage is raised again in order to close the needle-shaped injection valve member 9. The representation according to FIG. 1.2 shows in a schematic manner that the needle-shaped injection valve gHed 9 has the seat diameter i _s in the region of its seat in the end of the nozzle body 3 on the combustion chamber side.

An alternative embodiment variant of the variable actuator lift ratio proposed according to the invention can be seen from the illustration in FIG. 2.

According to the variant shown in Figure 2, the Vorhubhülse 13 is surrounded by another sleeve 24. Both the injector body 2 and the pre-stroke sleeve 13 as well as the further sleeve 24 are supported on the upper flat surface of the nozzle body 3. With the embodiment variant shown in FIG. 2, assembly tolerances extending in the radial direction can be compensated for. The clamping sleeve 4 connecting the nozzle body 3 and the injector body 2 to one another is not shown in the illustration according to FIG. 2.

In contrast to the embodiment variant shown in FIG. 1, the further spring element 21 that positions the second piston 14 (ÜB) has been removed. Rather, it can be seen from the illustration in FIG. 2 that the spring element 25 positioning the second piston 14 (ÜB) is now integrated in the hydraulic coupling space 23. Analogous to the embodiment variant of the solution proposed according to the invention shown in FIG. 1, the hydraulic coupling space 23 is defined by the inner cylinder surface of the forward stroke sleeve 13 and the end faces of the first piston 12 (ÜA) and the second piston 14 (ÜB). The spring element 25 integrated in the hydraulic coupling space 23 can be centered on a pin which is located on the end face of one of the pistons 12 or 14.

While the outer spring element 17 is supported directly on the injector body 2 in accordance with the embodiment variant shown in FIG. 1, the outer spring element 17 in the embodiment variant shown in FIG. 2 places the further sleeve 24 on the upper flat surface of the nozzle body 3. For the sake of completeness, it should be mentioned that the second piston 14 (ÜB) is actuated by the spring element 25 accommodated in the hydraulic coupling space 23 with its collar 26 against a flat surface in the nozzle body 3. Analogously to the illustration according to FIG. 1, the control chamber spring element 15 is located in the control chamber 20 and acts on the injection valve gHed 9, which can be embodied in the form of a needle.

The illustration according to FIG. 3 shows a further embodiment variant of the device for variable actuator stroke transmission. While, according to the embodiment variants shown in FIGS. 1 and 2, the second piston 14 is supported with its piston end face 19 or with its collar 26 on the nozzle body 3, the embodiment variant according to FIG. 3 shows that the second piston 14 is also supported on the injection valve member 9 can support. For this purpose, a peg-shaped extension is provided below the collar 26, which bears against the upper end face of the needle-shaped injection valve head 9. The collar 26 comprises an upper contact surface 27, opposite the lower end face of the pre-stroke sleeve 13, and a lower contact surface 28, which assigns the needle-shaped injection valve gHed 9. In the embodiment variant according to FIG. 3, the preliminary stroke sleeve 13 is acted upon by the inner spring element 16. In the embodiment variant shown in FIG. 3, the spring element 25 is received within the hydraulic coupling space 23 between the first piston (ÜA) and the second piston 14 (ÜB) and can optionally be centered by a pin.

In the illustration according to FIG. 4, the actuator forces and actuator strokes achievable by the step translation are compared with the forces or sleeves of a system without step translation.

Reference number 30 denotes the stroke profile of the injection valve head 9, with hm _a x the maximum stroke path of the injection valve head 9 inside the nozzle body 3 and h _v the defined distance between the collar 26 on the second piston 14 (ÜB) and the lower end face the pre-stroke sleeve 13. F _max denotes the maximum force to be exerted by the piezo actuator 8, which is required to lift the needle-shaped injection valve handle 9 out of the nozzle seat. According to the force-stroke curve 33 of the piezo actuator 8 shown in FIG. 4 with step transmission, the force to be applied by the piezo actuator 8 decreases to a quarter of the maximum force F _max until the distance h _{v is} reached, with h reaching until the distance h is reached _v the gear ratio i _! prevails. FIG. 4 furthermore shows that after the defined distance h _{v has been reached} up to the maximum opening position of the injection valve head, position h _max only a small actuator force has to be applied by the piezo actuator 8. The course of the force to be applied by the piezo actuator 8 is degressive. The force-stroke core of the piezo actuator 8 with step ratio is identified by reference number 33 in accordance with the proposal according to the invention. The force-stroke characteristic curve runs until the distance h _{v is reached} , ie the distance between the collar 26 of the second piston 14 (ÜB) and that of the lower end face of the pre-stroke sleeve, which is shown in FIG. 1 and detail X (FIG. 1.1) 33 approximately linear with a large gradient and also approximately linear from reaching the distance h _v , but with a significantly lower gradient. The simply hatched area in FIG. 4, spanned by the triangle between F _{ma »} hma, 0 represents the switching energy of an actuator without translation. Since the switching energy to be applied by the actuator determines its volume, an actuator characterized by the switching energy 32 according to FIG. 4 builds relatively large. In contrast, an actuator that requires the switching energy 35 - represented by the double hatched area according to FIG. 4 - builds accordingly smaller.

LIST OF REFERENCE NUMBERS

1 fuel injector

2 injector body (holding body) 3 nozzle body

4 adapter sleeve

5 tightening

6 high pressure connection

7 cavity 8 piezo actuator

9 Injector gHed (nozzle needle)

10 nozzle area

11 nozzle space inlet

12 First piston (ÜA) 13 Pre-stroke sleeve dv diameter of the pre-stroke sleeve

14 second piston (ÜB)

15 control room spring element

16 Inner spring element 17 Outer spring element

18 stop d _A diameter of the first piston 12 d _N diameter of the injector valve

19 piston face of second piston 14 h _v defined distance

20 control room

21 Another spring element

22 Compensating hole

23 Coupling space ds seat diameter injector gHed

24 Another sleeve

25 spring element coupling space

26 fret

27 Upper contact surface 28 Lower contact surface

30 Injection valve stroke stroke

31 actuator power

F _max maximum opening force 32 Actuator switching area without gear ratio

33 Force / stroke characteristic of the actuator with step ratio H _ma χ maximum stroke

34 Switching point of actuator translation

35 Switched energy area actuator with gear ratio

Claims

claims

1. Fuel injector for injecting fuel into the combustion chamber of an internal combustion engine with an injection valve gHed (9) which can be actuated directly via a piezo actuator (8) and which is accommodated in a nozzle body (3) and which is controlled into a closed position via a spring element (15) characterized in that a hydraulic booster arrangement (12, 14) is provided between the piezo actuator (8) and the injection valve head (9) for adapting the force to be applied by the piezo actuator (8) to the opening force profile of the injection valve member (9).

2. Fuel injector according to claim 1, characterized in that the booster arrangement has a first piston (12) and a second piston (14) which are hydraulically coupled to one another via a coupling space (23).

3. Fuel injector according to claim 1, characterized in that the translator arrangement (12, 14) comprises a sleeve-shaped guide body (13).

4. Fuel injector according to claim 3, characterized in that the sleeve-shaped guide body (13) is biased via an inner spring element (16) which is supported on the piezo actuator (8).

5. Fuel injector according to claim 2, characterized in that a piston (14) of the booster arrangement (12, 14) via a further spring element (21) arranged in a hydraulic space of the nozzle body (3) and via a in the control chamber (20 ) arranged control chamber spring element (15) or via the spring element (15) arranged in the control chamber (20) and a spring element (25) arranged in the coupling space (23).

6. Fuel injector according to claim 1, characterized in that when an opening pressure p _{ö of} the injector (9) on the booster arrangement (12, 14) is reached, a first transmission ratio ii = d _A ² / d _N ² acts, where d is the diameter of the first Piston (12) and d _{N represents} the diameter of the injector handle (9).

7. The fuel injector according to claim 1, characterized in that when a collar (26) of a piston (14) of the translator arrangement (12, 14) is applied to the sleeve-shaped guide body (13) on the translator arrangement (12, 14), the transmission ratio i ₂ = d _v ² / d _N ² acts, where dy denotes the diameter of the sleeve-shaped guide body (13) and d _N the diameter of the injector (9).

8. Fuel injector according to claim 3, characterized in that the sleeve-shaped guide body (13) is surrounded by a further sleeve (24).

9. Fuel injector according to claim 5, characterized in that the hydraulic space in the nozzle body (3) and the control space (15) are connected to one another via a flow connection (23) in the second piston (14).

10. Fuel injector according to claim 9, characterized in that the flow connection (23) is designed as a connection bore or groove.

11. Fuel injector according to claim 2, characterized in that the second piston (14) of the translation arrangement (12, 14) in the rest position either with its piston end face (19) on a flat surface of the nozzle body (3) or with a pin directly on the injection valve gHed ( 9) supports.