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A fuel injector for fuel-injection systems of internal combustion engines having a piezoelectric or magnetostrictive actuator, includes a hydraulic coupler which actuates a valve-closure member ( 3) formed on a valve needle. The valve-closure member cooperates with a valve-seat surface to form a val

A fuel injector for fuel-injection systems of internal combustion engines having a piezoelectric or magnetostrictive actuator, includes a hydraulic coupler which actuates a valve-closure member ( 3) formed on a valve needle. The valve-closure member cooperates with a valve-seat surface to form a valve-sealing seat. The coupler includes a master piston and a slave piston which are guided in bores of a guide sleeve. Located between the master piston and the slave piston is a pressure chamber filled with a hydraulic fluid. A corrugated tube is positioned around the guide sleeve which is sealingly joined to the master piston at one end and to the slave piston at the other end, and which seals a supply chamber for the hydraulic fluid from a surrounding fuel chamber.

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What is claimed is: 1. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat

What is claimed is: 1. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat; a hydraulic coupler, the actuator configured to actuate the valve-closure member via the coupler, the coupler including a master piston and a slave piston, which are guided in bores of a guide sleeve, and a pressure chamber filled with a hydraulic fluid located between the master piston and the slave piston; and a corrugated tube positioned around the guide sleeve and sealingly joined to the master piston at one end and to the slave piston at the other end, the corrugated tube sealing seal a supply chamber for the hydraulic fluid from a surrounding fuel chamber, wherein: the corrugated tube is radially yielding, and the corrugated tube has a reduced wall thickness and is flexurally soft due to the wall thickness. 2. The fuel injector as recited in claim 1, wherein the corrugated tube is joined to the master piston and the slave piston in force locking manner. 3. The fuel injector as recited in claim 2, wherein the corrugated tube has an initial stress which forces the master piston and the slave piston apart. 4. The fuel injector as recited in claim 1, wherein the master piston and the slave piston have different diameters. 5. The fuel injector as recited in claim 1, wherein a lift of the actuator is restricted by a stop. 6. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat; a hydraulic coupler, the actuator configured to actuate the valve-closure member via the coupler, the coupler including a master piston and a slave piston, which are guided in bores of a guide sleeve, and a pressure chamber filled with a hydraulic fluid located between the master piston and the slave piston; and a corrugated tube positioned around the guide sleeve and sealingly joined to the master piston at one end and to the slave piston at the other end, the corrugated tube sealing seal a supply chamber for the hydraulic fluid from a surrounding fuel chamber, wherein the slave piston and the guide sleeve are integrally formed. 7. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat; a hydraulic coupler, the actuator configured to actuate the valve-closure member via the coupler, the coupler including a master piston and a slave piston, which are guided in bores of a guide sleeve, and a pressure chamber filled with a hydraulic fluid located between the master piston and the slave piston; and a corrugated tube positioned around the guide sleeve and sealingly joined to the master piston at one end and to the slave piston at the other end, the corrugated tube sealing seal a supply chamber for the hydraulic fluid from a surrounding fuel chamber, wherein: a lift of the actuator is restricted by a stop, and the stop is formed on an actuator head. 8. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat; a hydraulic coupler, the actuator configured to actuate the valve-closure member via the coupler, the coupler including a master piston and a slave piston, which are guided in bores of a guide sleeve, and a pressure chamber filled with a hydraulic fluid located between the master piston and the slave piston; and a corrugated tube positioned around the guide sleeve and sealingly joined to the master piston at one end and to the slave piston at the other end, the corrugated tube sealing seal a supply chamber for the hydraulic fluid from a surrounding fuel chamber, wherein: a lift of the actuator is restricted by a stop, and the corrugated tube is integrally formed with a corrugated tube for sealing an actuator chamber from a fuel chamber which has a reduced wall thickness in a region of the coupler. 9. A fuel injector for a fuel injection system of an internal combustion engine, comprising: a piezoelectric or magnetostrictive actuator; a valve closure member formed on a valve needle, the valve closure member cooperating with a valve seat surface to form a valve sealing seat; a hydraulic coupler, the actuator configured to actuate the valve-closure member via the coupler, the coupler including a master piston and a slave piston, which are guided in bores of a guide sleeve, and a pressure chamber filled with a hydraulic fluid located between the master piston and the slave piston; and a corrugated tube positioned around the guide sleeve and sealingly joined to the master piston at one end and to the slave piston at the other end, the corrugated tube sealing seal a supply chamber for the hydraulic fluid from a surrounding fuel chamber, wherein a filling channel is provided in at least one of the master piston and the slave piston, the channel connecting the supply chamber to a surrounding chamber of the coupler, the filling channel sealed in a pressure tight manner by a sealing element. 10. The fuel injector as recited in claim 9, wherein the filling channel is formed in the master piston by filling bores and connects the supply chamber to an actuator chamber. 11. The fuel injector as recited in claim 10, wherein the sealing element is a ball pressed into one of the filling bores.