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A fuel injector having an injector body and a fuel inlet communicates with a high-pressure fuel source outside the injector body and including an actuator received in a hollow chamber from which a high-pressure inlet extends to an injection valve member. Depending on the pressure in the first hydrau

A fuel injector having an injector body and a fuel inlet communicates with a high-pressure fuel source outside the injector body and including an actuator received in a hollow chamber from which a high-pressure inlet extends to an injection valve member. Depending on the pressure in the first hydraulic chamber, fuel is injected into a combustion chamber of an internal combustion engine when the injection valve member lifts from a seat. The actuator acts directly upon a stepped piston which defines the first hydraulic chamber and actuates a control piston. The injection valve member is guided in the control piston.

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The invention claimed is: 1. In a fuel injector, having an injector body, having a fuel inlet which is in communication with a high-pressure fuel source outside the injector body, having an actuator received in a hollow chamber from which hollow chamber a high-pressure inlet extends to an injection

The invention claimed is: 1. In a fuel injector, having an injector body, having a fuel inlet which is in communication with a high-pressure fuel source outside the injector body, having an actuator received in a hollow chamber from which hollow chamber a high-pressure inlet extends to an injection valve member, and as a function of the pressure in a first hydraulic chamber, fuel is injected into the combustion chamber of an internal combustion engine when the injection valve member lifts out of a seat, the improvement comprising a stepped piston acted directly on by the actuator, and a control piston which moves relative to the stepped piston and in which the injection valve member is guided, a step of the stepped piston defining the first hydraulic chamber on a first end of the first hydraulic chamber and an end face of the control piston defining the first hydraulic chamber on a second end of the first hydraulic chamber, the first hydraulic chamber acting on the end face of the control piston, the stepped piston acting on a second hydraulic chamber, which second hydraulic chamber is embodied in the control piston and which communicates hydraulically with a third hydraulic chamber disposed in the control piston, wherein an end face of the injection valve member protrudes into the third hydraulic chamber, and wherein the stepped piston is embodied with a first diameter and a second diameter, the first diameter exceeds the second diameter, the first diameter is acted on by the actuator, and the second diameter acts on the second hydraulic chamber. 2. The fuel injector as defined by claim 1, further comprising an annular face on the step of the stepped piston defining the first hydraulic chamber, and a sleeve embracing the annular face. 3. The fuel injector as defined by claim 1, wherein the control piston comprises both the second hydraulic chamber and the third hydraulic chamber which communicate hydraulically with one another, and wherein the control piston is guided in a guide of the injector body. 4. The fuel injector as defined by claim 1, further comprises a mechanical driver disposed on the injection valve member and guided in a hollow chamber of the control piston movably between a first and a second stroke stop. 5. The fuel injector as defined by claim 1, further comprising a spring element disposed between a face end of the control piston and the injection valve member, the spring biasing the injection valve member into a defined outset position relative to the control piston. 6. The fuel injector as defined by claim 1, wherein the control piston comprises both the second hydraulic chamber and the third hydraulic chamber which communicate hydraulically with one another, and wherein the control piston is guided in a guide of the injector body, and wherein upon subjection of the actuator to voltage, by simultaneous subjection of the first hydraulic chamber and the second hydraulic chamber to pressure via the stepped piston the injection valve member guided in the control piston is pressed into its seat. 7. The fuel injector as defined by claim 1, the control piston comprises both the second hydraulic chamber and the third hydraulic chamber which communicate hydraulically with one another, and wherein the control piston is guided in a guide of the injector body, and wherein upon termination of subjection of the actuator to voltage, the first and second hydraulic chambers are simultaneously pressure-relieved and the third hydraulic chamber is pressure-relieved in delayed fashion, and wherein the control piston embraces a mechanical driver to move the injection valve member out of its seat. 8. The fuel injector as defined by claim 7, wherein the mechanical driver is disposed in a hollow chamber in the control piston, and wherein upon a delayed pressure relief of the third hydraulic chamber, the injection valve member automatically opens wider in accordance with the length of the hollow chamber. 9. In a fuel injector, having an injector body, having a fuel inlet which is in communication with a high-pressure fuel source outside the injector body, having an actuator received in a hollow chamber from which hollow chamber a high-pressure inlet extends to an injection valve member, and as a function of the pressure in a first hydraulic chamber, fuel is injected into the combustion chamber of an internal combustion engine when the injection valve member lifts out of a seat, the improvement comprising a stepped piston acted directly on by the actuator, and a control piston which moves relative to the stepped piston and in which the injection valve member is guided, a step of the stepped piston defining the first hydraulic chamber on a first end of the first hydraulic chamber and an end face of the control piston defining the first hydraulic chamber on a second end of the first hydraulic chamber, the first hydraulic chamber acting on the end face of the control piston, the stepped piston acting on a second hydraulic chamber, which second hydraulic chamber is embodied in the control piston and which communicates hydraulically with a third hydraulic chamber disposed in the control piston, wherein an end face of the injection valve member protrudes into the third hydraulic chamber, wherein the control piston comprises both the second hydraulic chamber and the third hydraulic chamber which communicate hydraulically with one another, and wherein the control piston is guided in a guide of the injector body, and wherein the second hydraulic chamber and the third hydraulic chamber communicate with one another via a conduit containing a throttle restriction. 10. The fuel injector as defined by claim 2, further comprising a plane face embodied on the injector body, and wherein the sleeve surrounding the stepped piston is braced with a bite edge which rests on the plane face. 11. The fuel injector as defined by claim 1, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 12. The fuel injector as defined by claim 2, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 13. The fuel injector as defined by claim 1, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 14. The fuel injector as defined by claim 3, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 15. The fuel injector as defined by claim 4, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 16. The fuel injector as defined by claim 5, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 17. The fuel injector as defined by claim 6, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 18. The fuel injector as defined by claim 7, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston. 19. The fuel injector as defined by claim 8, wherein opening of the injection valve member upon cancellation of subjection of the actuator to voltage is effected by means of pressure relief of the first hydraulic chamber, upon slaving of the injection valve member by the control piston, and by delayed pressure relief of the third hydraulic chamber in the control piston, while the injection valve member automatically moves in an opening direction relative to the control piston.