Further the present invention refers to a method of producing a piezoelectric injector unit.

Piezoelectric injector units comprising a piezoelectric as- sembly 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 ve- hicle 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 ele- ments designed for a certain purpose and configured according to certain parameters.

EP 95 912 885 Al 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 as- sembled 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 un- satisfying, 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 po- sitioned 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 ele- ment, is configured as an opening in the housing. Conse- quently, the whole housing has to be machined with high pre- cision, increasing the costs. Finally the disadvantages con- cerning the testing of the unit as mentioned earlier apply here, too.

It is an object of the present invention to provide a piezoe- lectric injector unit and a method for producing a piezoelec- tric injector unit which overcome the disadvantages of the prior art and in particular to provide a device that can ef- ficiently 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 im- proves an injector assembly according to the prior art by the valve needle and the metering opening being part of a func- tionally independent valve module; the actuator element being part of a functionally independent piezoelectric actuator

module; and both modules being-preferably reversibly-in- serted into the rigid housing.

This means that the injector unit is no longer considered as an individual device for an overall performance, but is sub- divided 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 inde- pendent assembly can be produced and tested individually be- fore insertion into the housing. Thus, errors can be detected in an early stage. Discarding an unsatisfying module is rela- tively cheap and does not involve disassembling and reassem- bling of the whole unit. The rigid housing can be machined in quite a simple and unsophisticated way, reducing the overall cost substantially.

In one preferred embodiment there are provided thermal com- pensator means for compensating thermal expansion of the pie- zoelectric actuator module, the thermal compensator means be- ing configured as a functionally independent thermal compen- sator 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 in- vention 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 hous- ing 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 enaines requesting different performances

of fuel injection one or more of the modules can be exchanged with modules designed according to different functional pa- rameters 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 inven- tion 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.

In a preferred embodiment the injector unit according to the present invention is provided with a valve module comprising 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.

In one advantageous embodiment of the present invention, the housing is comprising a longitudinal slit, in which the sup- ply tube connected to the valve module is sliding during in- sertion 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.

Preferably, the housing is provided with an opening, through which a terminal connector may be connected to the piezoelec- tric 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 mod- ule 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 ac- tuator 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 at- taching and adjusting adjusting means-prefeably an ad- justable 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.

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 consis- tently 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 be- fore 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 assem- bly.

In an advantageous variation of the method according to the present invention there is provided the further step of con- necting the valve module to a fuel supply tube prior to in- serting it into 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.

In an advantageous improvement of the method according to the present invention the fuel supply tube is sliding in a longi- tudinal slit when inserting the valve module into the hous- ing. This represents an astonishing easy and cost efficient way of implementing the idea explained in the preceding para- graph.

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 ac- cording 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 ac- cording to the invention. Fig. la illustrates a side view of the housing 10; Fig. 1b illustrates a longitudinal view of the housing 10; and Fig. lc illustrates another side view of the housing 10 from an opposite side with respect to Fig. la.

From Fig. 1b it can be seen, that the housing 10 is provided with a substantially cylindrical inner surface 11 represent- ing a cavity open at both ends into which correspondingly cy- lindrical elements can easily and reversibly be inserted from one side (left side in Fig. lb). At the other end of the housing 10 (right end in Fig. lb) there is provided a shoul- der 12, acting as an abutment member for items inserted into the housing 10.

As can be seen from Fig. lc, 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. lc) 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. la the hole 14 is surrounded by the housing's 10 wall at all sides. However, in other embodi- ments the hole 14 can also be configured as a slit.

Fig. 2 illustrates three modules 20,30, 40 ready for assem- bly. Module 20 is a piezoelectric actuator module comprising a piezoelectric element, which is used to move a piston ele- ment (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 meter- ing opening 31 according to the control voltage supplied to the actuator module 20. As the valve module 30 may be con- nected 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 ele- ment in the actuator module 20. However, if an actuator mod- ule is chosen such that the piezoelectric element is inter- nally compensated, no compensation module 40 is necessary.

Fig. 3 illustrates an exploded view of the injector unit ac- cording to the invention featuring the elements of Fig. 3 to- gether with the housing 10 of Fig. 1. When assembling the in- jector 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 cy- lindrical part with a diameter corresponding to the inner di- ameter 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 par

ticular 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 hous- ing, thus, adjusting the biasing force applied to the piezoe- lectric 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 hous- ing'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 numer- ous ways and may assume many embodiments other than that spe- cifically set out and described above. Accordingly, it is in- tended by the appended claims to cover all modifications of the invention which fall within the scope of the invention.