Fuel injector

Details Fuel injector Fuel injector

2000-04-28

2001-04-10

Brinson, Patrick (Department: 3752)

Fluid sprinkling, spraying, and diffusing

Including valve means in flow line

Reciprocating

C239S453000, C239S533700, C251S057000

Reexamination Certificate

active

06213414

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a fuel injector having an actuator for generating a lifting movement and a lift translator (lift transfer element) filled with a hydraulic medium and deformable in the lifting direction, for transferring the lifting movement of the actuator to a valve needle.
BACKGROUND INFORMATION
German Patent No. 195 00 706 describes a fuel injector. In this context, provision is made for a lift translator or travel transformer which converts a relatively small actuator travel, for example, of a piezoelectric actuator, into a longer lift of the valve needle. In this context, the expansion of the actuator is introduced into an amplifier chamber via a working piston of the lift translator, and transmitted to the valve needle via a lift piston, the valve executing a lift which is increased in the ratio of the piston areas bordering the amplifier chamber at the end faces. To compensate for temperature influences, wear, and manufacturing tolerances on the actuator travel, the amplifier chamber is provided with a defined leak, which is implemented by a ring gap between the piston and a valve-housing wall, and has a sufficiently high resistance to flow so that the movements of the actuator are transmitted to the valve needle in an essentially undamped manner. Used as hydraulic medium of the lift transmission is the fuel itself, diesel fuel in the case of German Patent No. 195 00 706. However, this creates the problem that the defined leak must be very small because of the low viscosity of the fuel. If the intention is for the known fuel injector to be used for Otto spark ignition engines, the further problem arises that the gasoline boils at comparatively low temperatures and can then no longer work as hydraulic medium because of the formation of bubbles.
SUMMARY OF THE INVENTION
The fuel injector according to the present invention has a compensating chamber for the hydraulic medium, the compensating chamber being connected to an interior space of the lift translator via a throttle opening and enclosed by a casing, and the fuel injector having the advantage that quasistatic deformations of the actuator because of temperature influences can be compensated for by an exchange of the hydraulic medium between the interior space of the lift translator and the compensating chamber. By choosing a sufficiently small throttle opening, however, the hydraulic medium contained in the lift translator acts as an incompressible liquid during the relatively fast actuator actuation so that the fast movements of the actuator are transmitted to the valve needle in an essentially undamped manner.
The fuel injector according to the present invention has the advantage that the hydraulic medium can be selected independently of the fuel so that the hydraulic medium can have a high boiling point and a relatively high viscosity. In this manner, the hydraulic medium can be prevented from evaporating. A higher viscosity permits a larger opening diameter of the throttle opening, which, because of this, can be manufactured in a simpler manner from a standpoint of production engineering.
The preferably elastic casing of the compensating chamber is preferably composed of a thin-walled metal body which is welded to the lift translator in a liquid-tight manner. The compensating chamber can radially surround a small-diameter section of the lift translator, thereby enabling a compact design.
The outer wall of the lift translator is preferably designed as a bellows. This has the advantage for the outside wall to be deformable only in the lifting direction and not in the radial direction. Because of this, the lifting movements of the actuator are transmitted to the valve needle without damping.
Suitable as hydraulic medium is a liquid which boils at high temperature so that the hydraulic medium is prevented from evaporating. The diameter of the throttle opening is preferably selected as a function of the viscosity of the hydraulic medium in such a manner that the lifting movement of the actuator is transmitted in an essentially undamped manner; however, quasistatic deformations are compensated for by exchange of the hydraulic medium with the elastic compensating chamber.
The actuator is preferably a stacked piezoelectric actuator permitting lifting movements which are defined in time and space.
The fuel injector according to the present invention is particularly suitable for an injection system for an Otto spark ignition engine, since gasoline is not suited as hydraulic medium of the lift transmission because of the low boiling point.


REFERENCES:
patent: 4322055 (1982-03-01), Baumann
patent: 4728074 (1988-03-01), Igashira et al.
patent: 5417142 (1995-05-01), Lohmann
patent: 5803361 (1998-09-01), Horiuchi et al.
patent: 195 00 706 (1996-07-01), None

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