EP1493917B1

EP1493917B1 - Injector assembly

Info

Publication number: EP1493917B1
Application number: EP20030012438
Authority: EP
Inventors: Angelo D'arrigo
Original assignee: Siemens VDO Automotive SpA
Current assignee: Continental Automotive Italy SpA
Priority date: 2003-05-30
Filing date: 2003-05-30
Publication date: 2006-04-12
Anticipated expiration: 2023-05-30
Also published as: DE60304569T2; EP1493917A1; WO2004106727A1; DE60304569D1

Description

The present invention refers to a piezoelectric injector unit, in particular for injecting fuel into a vehicle engine, comprising a housing containing a valve needle for opening and closing a valve orifice and a metering opening, respectively and a piezoelectrically driven actuator element for actuating the valve needle according to an electrical control voltage.
Further the present invention refers to a method of producing a piezoelectric injector unit.
Piezoelectric injector units comprising a piezoelectric assembly for actuating a valve assembly are commonly used in modern motor vehicles for controlling the injection of fuel in to the vehicle engine. The injection of fuel in to the vehicle engine can be performed fast and with high precision by means of a piezoelectric element moving a piston element, that is actuating a valve needle, which in turn opens and closes a metering opening accordingly.
So far injector units have been considered as individual elements designed for a certain purpose and configured according to certain parameters.
EP 95 912 885 A1 discloses a typical injector unit according to prior art. Different and very individually shaped sections of outer and inner, movable and fixed elements have to be assembled and sealed to make up the total unit.
The main disadvantage of this prior art is that only the whole device, i.e. the injector unit as such can be tested for its functional quality. If its overall performance is unsatisfying, either the whole unit has to be discarded or every single one of its elements has to be exchanged one by one to find the error, each time necessitating a complete disassembling and reassembling of the whole unit, thereby adding further error sources.
EP 1 046 809 A2 discloses an injection unit with a one piece housing, in which the single elements like the valve needle, different springs, seals, abutment elements etc. have to positioned and fixed. The assembling is, thus, very cumbersome and expensive. Also, the housing containing a separate fuel supply channel within its housing is difficult to machine. Further, the metering opening, which is a high precision element, is configured as an opening in the housing. Consequently, the whole housing has to be machined with high precision, increasing the costs. Finally the disadvantages concerning the testing of the unit as mentioned earlier apply here, too.
US 2003/0042325 A1 discloses a piezoelectric injector unit for injecting fuel into a vehicle engine comprising a housing containing a valve needle for opening and closing a metering opening and a piezoelectrically driven actuator element for actuating the valve needle according to an electrical control voltage. The valve needle and a valve body which comprises a recess to take in the needle form a functionally independent module. The injector further comprises a piezoelectric actuator module. The valve module and the piezoelectric actuator are both located in a housing.
EP 1 245 828 A1 discloses a method of fabricating and testing a modular fuel injector with an electromagnetic actuator. A fuel module comprises a valve body, a seat and a guide armature comprising a needle, a pole piece, a spring, a filter and an inlet tube. The fuel module is tested prior to pushing an overmolded power group, forming at the same time the housing, over the fuel module. The overmolded power group has the function of the housing and also comprises part of the actuator, in particular it comprises the coils for the electromagnetic actuator.
It is an object of the present invention to provide a piezoelectric injector unit and a method for producing a piezoelectric injector unit which overcome the disadvantages of the prior art and in particular to provide a device that can efficiently be tested and assembled easily and at reduced cost as well as to provide a method to do so.
This object is obtained by the features of the independent claims.
Preferred embodiments of the present invention are defined by the depending claims.
The injector assembly according to the present invention improves an injector assembly according to the prior art by the valve needle and the metering opening being part of a functionally independent valve module; the actuator element being part of a functionally independent piezoelectric actuator module; and both modules being - preferably reversibly - inserted into the rigid housing.
This means that the injector unit is no longer considered as an individual device for an overall performance, but is subdivided in accordance to its different subfunctions. Each subfunction is represented by a module of its own, which is configured as a functionally independent assembly. Each independent assembly can be produced and tested individually before insertion into the housing. Thus, errors can be detected in an early stage. Discarding an unsatisfying module is relatively cheap and does not involve disassembling and reassembling of the whole unit. The rigid housing can be machined in quite a simple and unsophisticated way, reducing the overall cost substantially.
The valve module comprises a connection port to a fuel supply tube. This has the effect that the fuel does not flood the whole housing, but only the valve module. Thus, only the valve module has to be sealed, which facilitates the machining of the housing even further.
The housing comprises a longitudinal slit, in which the supply tube connected to the valve module is sliding during insertion of the valve module into the housing. By means of this feature it becomes possible to insert into the housing a valve module that has been tested according to its function and sealing with changes of its configuration, that might give rise to further errors.
In one preferred embodiment there are provided thermal compensator means for compensating thermal expansion of the piezoelectric actuator module, the thermal compensator means being configured as a functionally independent thermal compensator module and being inserted into the housing together with the piezoelectric actuator module and the valve module. Although there are piezoelectric actuator assemblies known comprising integrated thermal compensation means, it is a consistent continuation of the basic idea of the present invention to subdivide such combination unit into different units with particular tasks, namely an actuator unit and a compensator unit, yielding analogue advantages as explained above.
A further preferred embodiment is characterized by the housing having a partially cylindrically shaped interior, the modules having a partially cylindrically shaped exterior, and the inner cylinder diameter of the housing corresponding to the outer cylinder diameter of the modules. This makes the housing universally applicable to different kinds of modules. I.e. for different engines requesting different performances of fuel injection one or more of the modules can be exchanged with modules designed according to different functional parameters but having the same outer shape. These different modules can easily be inserted into the universal housings and can be combined with other matching modules.
Preferably, the injector unit according to the present invention is provided with a housing having an adjustable cap, by means of which the modules inserted in the housing may be pressed together by an adjustable force. This corresponds to an easy way of calibrating the injector unit providing a bias force to the piezoelectric element.
Preferably, the housing is provided with an opening, through which a terminal connector may be connected to the piezoelectric actuator module after its insertion into the housing. It is necessary to have at least one electrical supply line fed through the housing in order to supply the piezoelectric module with the control voltage. As an electrical connection is not difficult to fit and does not involve serious error sources, this connection can be provided after the mechanical assembly of the injector unit. Thus a simple hole through the housing's wall can be appropriate.
The method of production according to the present invention is comprising the steps of

providing a functionally independent valve module;
providing a functionally independent piezoelectric actuator module;
providing a rigid housing positively matching the outer shape at least of parts of the modules,
inserting the modules into the housing; and
pressing together the modules by a defined force by attaching and adjusting adjusting means - prefeably an adjustable cap - to the housing.

The main advantages of this method have been explained above in the context of the injector unit according to the present invention. The method allows for an optimised production of the separate modules and an easy assembly even by unskilled workers or simple machines. The modules can be produced in high production numbers, thus lowering the price for every single module. Also changes in parameters, that are necessary for meeting the requirements of different engines do not change the assembly and calibration of the total unit.
In a further step the valve module is connected to a fuel supply tube prior to inserting it in the housing. Thus, the valve module can be tested according to its true function and its configuration may be left unchanged when assembling the total unit.
The fuel supply tube slides in a longitudinal slit when inserting the valve module into the housing. This represents an astonishing easy and cost efficient way of implementing the idea explained in the preceding paragraph.
A preferred embodiment of the present invention comprises the further step of providing and inserting into the housing a functionally independent thermal compensator module. Thus, as explained above, the basic idea of the invention is consistently continued and the function carried out by the device produced by the method of the invention is further subdivided into its elementary functions.
It is preferred that each module is tested independently before inserting it into the housing. Thus, when a failure of a module is detected, this module can be repaired or exchanged without having to disassemble the whole unit. If, however, the total unit is not working satisfactory, the reason must be found in a defect housing or an erroneous step of assembly.
In the following the present invention will be explained in more detail with respect to the drawings, in which

Fig. 1: illustrates three different views of a housing according to the invention;
Fig. 2: illustrates three modules ready for assembly;
Fig. 3: illustrates an exploded view of the injector unit according to the invention; and
Fig. 4: illustrates an assembled injector unit according to the invention.

Fig. 1 illustrates three different views of a housing 10 according to the invention. Fig. 1a illustrates a side view of the housing 10; Fig. 1b illustrates a longitudinal view of the housing 10; and Fig. 1c illustrates another side view of the housing 10 from an opposite side with respect to Fig. 1a. From Fig. 1b it can be seen, that the housing 10 is provided with a substantially cylindrical inner surface 11 representing a cavity open at both ends into which correspondingly cylindrical elements can easily and reversibly be inserted from one side (left side in Fig. 1b). At the other end of the housing 10 (right end in Fig. 1b) there is provided a shoulder 12, acting as an abutment member for items inserted into the housing 10.
As can be seen from Fig. 1c, the housing 10 is provided with a longitudinal slit 13 cut into the housing's 10 wall. This slit is used, as explained further below, as a slideway for the valve module and the connected fuel tube. At one end of the housing 10 (left end in Fig. 1c) the slit 13 is open to allow the insertion of modules.
Opposite to the slit 13 there is provided a hole 14, through which an electrical terminal connector can be inserted. In the embodiment shown in Fig. 1a the hole 14 is surrounded by the housing's 10 wall at all sides. However, in other embodiments the hole 14 can also be configured as a slit.
Fig. 2 illustrates three modules 20, 30, 40 ready for assembly. Module 20 is a piezoelectric actuator module comprising a piezoelectric element, which is used to move a piston element (both elements not explicitly shown in Fig. 2) depending on an electrical control voltage supplied thereto.
When assembled and actuated the piston element acts onto a movable acting element of the valve module 30. The acting element can be the valve needle 32 of the valve module 30 or any other linking element. However, the valve element 30 is configured such, that, upon actuation by the actuator module 20, the valve needle 32 is moved to open and close the metering opening 31 according to the control voltage supplied to the actuator module 20. As the valve module 30 may be connected to a fuel reservoir or pump by means of the fuel tube 33 and a tube connector 34, the opening and closing of the metering opening 31 yield a well metered injection of fuel to a vehicle engine.
Finally there is provided a thermal compensation module 40 for compensating thermal expansion of the piezoelectric element in the actuator module 20. However, if an actuator module is chosen such that the piezoelectric element is internally compensated, no compensation module 40 is necessary.
Fig. 3 illustrates an exploded view of the injector unit according to the invention featuring the elements of Fig. 3 together with the housing 10 of Fig. 1. When assembling the injector unit, first the valve assembly is inserted into the housing, while the fuel tube is sliding in the slit 13. The outer shape of the valve module 30 is chosen such that a cylindrical part with a diameter corresponding to the inner diameter of the housing 10 is kept in slight contact to walls of the housing 10 and is abutted by the shoulder 12. The front part of the valve module 30, however, is fed through the opening of the housing 10 and represents the tip of the total injector unit. Further, the actuator module 20 and the thermal compensation module 40 are inserted similarly into the housing 10.
In order to prevent the modules 20, 30, 40 from sliding out of the housing 10 again, the insertion end of the housing 10 (left end in Fig. 3) is closed by an adjustable cap, in particular by a ring nut 15. The ring nut 15 can also be used to calibrate the injection unit by adjusting the force by which the modules 20, 30, 40 are pressed together inside the housing, thus, adjusting the biasing force applied to the piezoelectric element of the actuator module 10.
In order be able to supply a suitable control voltage to the actuator module 20, an electrical terminal connector 21 can be coupled to the module 20 through the hole 14 in the housing's 10 wall.
Fig. 4 illustrates an assembled injector unit according to the invention.
While the invention has been described in the context of a preferred embodiment, it will be apparent to those skilled in the art that the present invention may be modified in numerous ways and may assume many embodiments other than that specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the scope of the invention.

Claims

A piezoelectric injector unit, in particular for injecting fuel into a vehicle engine, comprising a housing (10) containing a valve needle (32) for opening and closing a metering opening (31) and a piezoelectrically driven actuator element for actuating the valve needle (32) according to an electrical control voltage
characterised in that
- the valve needle (32) and the metering opening (31) being part of a functionally independent valve module (30) :

- the actuator element being part of a functionally independent piezoelectric actuator module (20);

- both modules being inserted into the rigid housing (10);

- the valve module (30) comprising a connection port to a fuel supply tube (33);

- the housing (10) comprising a longitudinal slit (13), in which the fuel supply tube (33) connected to the valve module (30) is sliding during insertion of the valve module (30) into the housing (10).
The injector unit according to claim 1,
characterised by
thermal compensator means for compensating thermal expansion of the piezoelectric actuator module (20), the thermal compensator means being configured as a functionally independent thermal compensator module (40) and being inserted into the housing (10) together with the piezoelectric actuator module (20) and the valve module (30).
The injector unit according to one of the preceding claims,
characterised in that
the housing (10) having a partially cylindrically shaped interior, the modules (20, 30, 40) having a partially cylindrically shaped exterior, and the inner cylinder diameter of the housing (10) corresponding to the outer cylinder diameter of the modules (20, 30, 40).
The injector unit according to one of the preceding claims,
characterised in that
the housing (10) having an adjustable cap (15), by means of which the modules (20, 30, 40) inserted into the housing (10) may be pressed together by an adjustable force.
The injector unit according to one of the preceding claims,
characterised by
an opening (14) in the housing, through which an electrical terminal connector (21) may be connected to the piezoelectric actuator module (20) after its insertion into the housing (10) .
A method for producing a piezoelectric injector unit, in particular for injecting fuel into a vehicle engine, comprising the steps of
- providing a functionally independent valve module (30);

- providing a functionally independent piezoelectric actuator module (20);

- providing a rigid housing (10) positively matching the outer shape at least of parts of the modules (20, 30),

- connecting the valve module (30) to a fuel supply tube (33), with the fuel supply tube (33) sliding in a longitudinal slit when inserting the valve module (30) into the housing (10);

- inserting the modules (20, 30) into the housing (10); and

- pressing together the modules (20, 30) by a defined force by attaching and adjusting adjusting means (15) to the housing.
The method according to claim 6,
characterised by
the further steps of providing and inserting into the housing (10) a functionally independent thermal compensator module (40) .
The method according to claim 6 or 7,
characterised by
the further step of testing each module (20, 30, 40) independently before inserting it into the housing (10).