Fuel injection valve

A fuel injection valve having a piezoceramic valve body, comprising a plurality of superposed ceramic plates each having one conductor layer on each side and voltage leads to the conductor layers. Each ceramic plate is arranged on a carrier plate. Between each unit, consisting of a ceramic plate and a carrier plate, an insulating foil is provided with conductor foils arranged on each side as conductor layers. Each insulating foil comprises two terminal lugs. Each insulating foil, in the region of a terminal lug, is laminated on one side with one conductor foil. The correlated termial lugs are connected in each case to an electrical contact for the correlated conductor foils.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a fuel injection valve having a piezoceramic valve 
body, comprising a plurality of superposed ceramic plates each having one 
conductor layer on each side and voltage leads to the conductor layers. 
2. Description of the Prior Art 
A fuel injection valve of the said type has been described in the DE-OS No. 
24 02 085. Therein adjacent ceramic bodies are provided on both sides with 
conductor layers and are separated from one another by one insulating 
layer each. The conductor layers are connected to electrodes. A connection 
of such conductor layers to electrodes is difficult and complicated. 
The DE-OS No. 17 51 543 describes a fuel injection valve, wherein a 
metallic carrier plate carries ceramic plates. Same are oppositely 
polarized each; thereby unsymmetries and variations of the setting paths 
of the valve are caused. Also in this case the voltage connection to the 
carrier plate is critical. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a mechanically stable and durable 
contacting of the conductor foils in order to achieve a long useful life. 
According to the invention this object is solved in that each ceramic plate 
is arranged on a carrier plate, that between each unit, consisting of a 
ceramic plate and a carrier plate, an insulating foil is provided with 
conductor foils arranged on each side as conductor layers, that each 
insulating foil comprises two terminal lugs, that each insulating foil, in 
the region of a terminal lug, is laminated on one side with one conductor 
foil, and that the correlated terminal lugs are connected in each case to 
an electrical contact for the correlated contact foils. 
The invention differs from the prior art in that the conductor foils for 
the voltage supply to the carrier plate and to the ceramic plate are 
formed in each case with an insulating foil as compound foil so that the 
conductor arrangement has a firm coherence. This enables a stable and 
durable voltage connection. It is possible by this arrangement to operate 
the individual ceramic plates in equal orientations so that an exact 
position-dependent control is possible. The terminal lugs of the 
insulating and conductor foils can be contacted easily and durably. 
A secure contacting is reached in that the correlated terminal lugs are 
folded at their ends with exposed conductor foil and are stacked one upon 
the other on a contact pin. By this folding it is guaranteed that in each 
case the conductor foils of adjacent terminal lugs are superposed in 
immediate electrical contact so that a safe contacting is guaranteed. 
A further object of the invention is directed to a compact arrangement of 
the foils in that each insulation foil with the two conductor layers forms 
a compound foil. 
In order to stabilize the pile of plates it is provided that the pile of 
plates consisting of carrier plates, ceramic plates, and compound foils be 
flanked by a metal plate at each side. 
The fuel injection valve is further characterized in that the pile of the 
plates is situated on a valve stem supporting a valve needle and is 
clamped between a spring and a supporting shoulder of the valve stem, that 
the pile is positioned on a shoulder of the valve housing and is 
compressed by means of a pressure spring against this shoulder in the 
closing direction of the valve needle. This arrangement renders possible 
an advantageous construction in that the border of the pile of plates is 
supported within the valve housing and is compressed in the closing 
direction of the valve needle. 
In order to guarantee proper adjustment of the closing pressure and a 
secure contact feed, it is provided that within the valve housing a 
supporting plate is arranged, on which, on the one hand, the pressure 
spring is supported and which, on the other hand, receives the contact 
pins.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The fuel injection valve comprises a valve housing 1 with a cover 2 and an 
injection nozzle 3. Within the injection nozzle 3 an injection channel 4 
is provided, which is closed by a valve closure 5 situated on a valve stem 
6. Within the cover a fuel supply channel 7 as well as a filter body 8 are 
provided. In addition, a plug-in connection 9 with two contact members or 
pins 10, 11 is provided. 
Within the valve housing the piezoceramic valve body 12 is provided, the 
structure of which will be described in detail with reference to FIGS. 3 
and 4 and which serves as a means for moving the stem 6 with reference to 
the housing 1. The valve body 12 is built up in the form of a plate 
package. A plurality of metallic plate-like carriers 13 support each a 
ceramic plate 14. Each ceramic plate 14 is firmly bonded to the respective 
carrier 13 in accordance with a conventional method. Between these first 
laminations including the plates 14 and carriers 13, in each case for the 
electrical contacting, second laminations in the form of compound foils 
are arranged, which consist of an insulating foil 15 with metallic 
conductor foils or layers 16 laminated on both sides. In the inner region 
of the pile of plates the insulating foils 15 are laminated on both sides 
in the manner as described. The outermost insulating foils 151 and 152 are 
laminated just on one side with a conductor foil 16. The pile or stack of 
first and second laminations is flanked by metal plates 17, 18. 
The metal plate 17 is situated, on the one side, on a shoulder or abutment 
19 of the valve stem 6 and, on the other side, on a shoulder or abutment 
20 of the valve housing 1. In the region of the shoulder 20 channels 21 
for the fuel are provided. On the metal plate 18 a first biasing means in 
the form of a diaphragm spring 22 is supported, which is kept in a groove 
23 of the valve stem 6. This spring 22 keeps the plate package, or the 
valve body 12, respectively, together, in order to guarantee a sufficient 
electrical contacting between the conductor foils 16 and the carrier 
plates 13 or the ceramic plates 14, respectively. 
Within the valve housing 1 a supporting member in the form of a plate 24 is 
arranged, on which a second biasing means in the form of a helical 
pressure spring 25 is supported. This helical pressure spring 25 bears 
against the diaphragm spring 22 and provides the closing pressure for the 
valve closure 5 i.e., it urges the closure 5 to its closing position. 
Each insulating foil 15, laminated on both sides, comprises two terminal 
lugs 26, 27. The terminal lugs 26 are laminated, on one side, with the 
conductor foil 16 of one voltage polarity. According to FIG. 3 this is the 
positive voltage polarity. The outermost insulating foil 151 comprises 
just one terminal lug according to the said polarity. The termincal lugs 
26 are folded each at the end so that in the region of this folding 28 the 
conductor foil 16 is situated on the outside. These foldings 28 are 
superposed and are placed on the contact pin 11 of the corresponding 
polarity. Thus, in each case conductor foils of adjacent insulating foils 
are placed one upon the other. Thereby a secure conducting connection is 
guaranteed. The contact pin 11 is fastened in the supporting plate 24 and 
fixed. 
The conductor foils of opposite polarity are led via the terminal lugs 27 
to the contact pin 10 as shown in FIG. 4. Also in this case an insulating 
foil 152 comprises just one terminal lug 27. Also in this case the 
foldings 28 are provided at the end. 
The individual ceramic plates of the pile of plates are electrically 
connected in parallel so that each ceramic plate supplies a precisely 
defined amount to the opening force. It is possible to provide by a 
specific quantity of the ceramic plates every opening force. It is also 
possible to realize a desired characteristic line by a specific 
dimensioning of the individual ceramic plates. Thus, an arrangement 
according to the invention renders possible a practical structure of a 
fuel injection valve with a piezoceramic valve body. The connecting 
technique with conductor foils and insulating foils enables assembly 
without difficulty. In this manner the difficulties of the conventional 
contacting methods for ceramic plates are avoided.