Piezo-control valve for fuel injection systems of internal combustion engines

In a piezo-control valve for fuel injection systems of internal combustion engines wherein a piezo-ceramic actuating rod is mounted with one end firmly to one end of a valve housing having a nozzle body with a valve seat disposed at the other end and a nozzle control needle is disposed in the nozzle body and pressed by the piezo-ceramic actuating rod onto the valve seat in the nozzle body when the piezo-ceramic actuating rod is not activated, the valve housing includes a sleeve-like portion disposed around the piezo-ceramic actuating rod which consists of a material compensating for temperature-caused changes in the length of the piezo-ceramic actuating rod.

BACKGROUND OF THE INVENTION 
The invention relates to a piezo-control valve having an end nozzle for 
fuel injection systems of internal combustion engines and a piezo-ceramic 
structure which is supported in a valve housing and has a needle-like 
closing portion seated on a valve seat and cooperating with a piezo 
actuation rod firmly mounted in the valve housing end remote from the end 
nozzle such that the needle-like closing portion is lifted off the valve 
seat when the piezo actuation rod is activated. 
A magnetostrictive or piezo-ceramic fuel injection valve with a closing 
member disposed on a valve seat is known for example from DE 29 31 874 C2. 
The valve includes a magnetostrictive rod which has a valve closing end 
and which, at the opposite end, is connected to a support structure 
capable of moving axially and dampening axial movements so that the rod is 
somehow floatingly supported whereby different heat expansion of the valve 
housing and the arrangement controlling the valve lift can be 
accommodated. 
However, with this arrangement, the valve lift may vary somewhat depending 
on the temperature so that a particular control signal does not always 
generate the same valve lift. 
It is the object of the present invention to provide a simple and 
space-saving piezo-control valve of the type referred to above wherein the 
valve lift which corresponds to the engine requirements is always the same 
independently of temperature changes. 
SUMMARY OF THE INVENTION 
In a piezo-control valve for fuel injection systems of internal combustion 
engines wherein a piezo-ceramic actuating rod is mounted with one end 
firmly to one end of a valve housing having a nozzle body with a valve 
seat disposed at the other end and a nozzle control needle is disposed in 
the nozzle body and pressed by the piezo-ceramic actuating rod onto the 
valve seat in the nozzle body when the piezo-ceramic actuating rod is not 
activated, the valve housing includes a sleeve-like portion disposed 
around the piezo-ceramic actuating rod which consists of a material 
compensating for temperature-caused changes in the length of the 
piezo-ceramic actuating rod. 
With the arrangement according to the invention the valve housing is 
expanding essentially at the same rate as the rod-like piezo-ceramic 
actuating rod whereby, in addition to achieving the high control speed 
required for today's internal combustion engines, the injection pattern 
can be controlled in an accurate manner particularly with extremely high 
pressure systems such as common rail fuel injection systems.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A piezo-control valve 1 for a fuel injection system such as a Diesel engine 
injection system comprises essentially an elongated valve housing 5, a 
piezo ceramic device 2 disposed in the valve housing 5 and a nozzle body 3 
with a nozzle control needle 4 axially movably disposed in the nozzle body 
3. The valve housing 5 is a sleeve-like member preferably consisting of 
two coaxial sleeve parts 5a, 5b which consist of materials with different 
heat expansion coefficients. 
The piezo-ceramic device 2 includes a rod-like piezo actuator 6 whose one 
end is disposed adjacent the nozzle control needle 4 and whose opposite 
end is firmly mounted on a disc-like end piece 7 which is supported at the 
adjacent end of the sleeve part 5a and fixed by a pin 8 so as to be 
non-rotatable with respect to the sleeve part 5a. The disc-like end piece 
7 is firmly mounted onto the free end of the sleeve part 5a by means of a 
cup nut 9. 
At its end adjacent the control needle 4, the piezo-actuator 6 which 
contracts when activated is firmly connected to an intermediate member 10. 
The front face 10a of this intermediate member 10 and the end face 5c of 
the housing sleeve part 5b are ground so as to be flush with respect to 
each other. The end face 4a of the nozzle control needle 4 and the front 
end 3a of the nozzle body 3 adjacent the intermediate member front face 
10a are also ground flush. 
In order to prevent fuel leakage along the valve seat 13 when the piezo 
actuator 6 is seated on the nozzle control needle 4 via the intermediate 
member 10 the nozzle control needle 4 must be engaged with the valve seat 
13 with a force which is higher than the lifting force generated by the 
fuel pressure. This is achieved by threading the component assembly 5, 7, 
9, 6, 10 onto the nozzle body 3 such that the front face 10a of the 
intermediate member 10 firmly presses the control needle 4 onto the valve 
seat 13 by way of an intermediate disc 11. The sleeve part 5b and the 
nozzle body 3 are in engagement with one another by way of an intermediate 
washer 12 which is thinner than the intermediate disc 11 by a 
system-specific accurate amount which in the present case is 0.035 mm. 
This amount causes an elastic compression of the piezo actuator which 
generates the required seating force for the control needle 4. 
The reference numeral 14 designates a fuel supply passage which leads to a 
pressure space 15 formed between the nozzle control needle 4 and the 
nozzle body 3. The two part valve housing sleeve 5 consists of different 
materials. Specifically, the lower sleeve part 5b consists of normal steel 
whereas the upper sleeve part 5a consists of Invar. 
In order to achieve essentially the same temperature expansion for the 
piezoactuator 6 at one hand and the two-part valve housing sleeve on the 
other, the axial lengths of the sleeve part 5b of steel and the sleeve 
part 5a of Invar are so selected that the sum of the heat expansion of the 
sleeve parts 5a and 5b corresponds to the heat expansion of the piezo 
actuator 6, that is, the heat expansion of the sleeve parts 5a and 5b 
compensates for the heat expansion of the rod-like piezo actuator 6. 
Instead of the two part valve housing sleeve, a single part valve housing 
sleeve can be utilized which consists of a material having a heat 
expansion coefficient corresponding to that of the piezo actuator rod 6.