17  EP 2 100 020 B1 18  age (U$_{0}$) corresponding to a first operating state of the injection valve (10) to a target voltage (U$_{1}$) cor- responding to a second operating state of the injec- tion valve (10),  characterized in that  in the first op- erating state the valve needle (13) rests on a valve seat (14a) in such a way that the injection valve (10) is closed, and at the output voltage (U $_{0}$) the actuator (12) has a first length, and  in that  the actuator (12) isdischarged by the predefinable voltage swing ( Δ U) to the targetvoltage (U $_{1}$), wherein saidactuator (12) shortens to a second length which is shorter than the first length in order to change the injection valve (10) from its closed state into its open state,  in that during the opening of the injection valve (10) and before a needle/stop (14b) which corresponds to a completely open state of the injection valve (10) is reached the valve needle (13) applies a reaction to the actuator (12) which increases the actuator volt- age (U) by a reaction voltage ( Δ U$_{R}$), and  in that  the voltage swing ( Δ U) is selected such that a desired reaction voltage ( Δ U$_{R}$) is produced, wherein the re- action ofthevalve needle (13)applied tothe actuator (12)iscaused  inthat  the valve needle (13)also firstly moves further onto the actuator (12) after the end of the energization ofthe actuatorand the valve needle (13) applies a corresponding force to the actuator (12), which is essentially stationary after the end of energization, which force controls the piezoelectric effectinaccordance withthe reaction voltage( Δ U$_{R}$). its opened state into its closed state, is regulated. 2. Method according to Claim 1,  characterized in that the actuator (12) is recharged in a predefinable re- charging time with a recharging current which is de- pendent on the voltage swing ( Δ U). 3. Method according to Claim 1,  characterized in that the reaction voltage ( Δ U$_{R}$)isselected forthe opening process of the injection valve (10) as a function of a predefinable time. 4. Method according to one of the preceding claims, characterized in that  the voltage swing ( Δ U) is se- lected such that the valve needle (13) reaches the valve seat(14a)and/ora/the needle/stop(14b)when the energization of the actuator (12) is ended. 5. Method according to Claim 4,  characterized in that the voltage swing ( Δ U) is selected such that an ab- solutevalue ofthe firsttimederivative oftheactuator voltage (U)becomes minimalbetween anend ofthe energization of the actuator (12) and a first change ofsign ofthe first time derivative ofthe actuator volt- age (U) since the end of the energization of the ac- tuator (12). 6. Method according to one of the preceding claims, characterized in that  a recharging time, which is necessary for changing the injection valve (10) from 7. Method according to Claim 6,  characterized inthat the recharging time is selected as a function of a desired closing time within which the valve needle (13)moves froman initialposition ontoits valve seat (14a). 8. Method according to one of the preceding claims, characterized inthat  the voltageswing ( Δ U)ispref- erably regulated for each operating cycle of the in- jection valve (10). 9. Method according to one of Claims 1 to 8,  charac- terized in that a) the regulation of the reaction volt- age ( Δ U$_{R}$) and/or b) the regulation of the first time derivative (U)ofthe actuatorvoltage (U)takes place between the end of the energization of the actuator (12) and a first change of sign of the first time deriv- ative (U) of the actuator voltage (U) since the end of the energization of the actuator (12) and/or c) the regulation of the closing time takes place in every n- thoperating cycle ofthe injection valve (10),wherein n > 1. · · 10. Computer program,  characterized in that  it is pro- grammed to carry out the method according to one of Claims 1 to 9. 11. Control device (20) for a fuel injection valve (10), in particularofan internalcombustion engine ofamotor vehicle,  characterized inthat  itisdesigned to carry out the method according to one of Claims 1 to 9. 1. Procédé pour fairefonctionnerune soupaped’injec- tion (10), en particulier une soupape d’injection de carburantd’unmoteurà combustioninterne d’un vé- hicule automobile, la soupape d’injection (10) pré- sentantun actionneurpiézoélectrique (12)pourl’en- traînement d’un pointeau de soupape (13) accouplé de préférence hydrauliquement à l’actionneur (12), l’actionneur (12), partant d’une tension initiale (U$_{0}$) correspondant à un premier état de fonctionnement de lasoupape d’injection (10),étantcommuté,c’est- à-dire étant chargé ou déchargé, d’une course de tension prédéfinissable ( Δ U)à une tension cible (U $_{1}$) correspondant à un deuxième état de fonctionne- ment de la soupape d’injection (10),  caractérisé en ce que  lepointeau de soupape (13),dans lepremier état de fonctionnement,repose surun siège desou- pape (14a) de telle sorte que la soupape d’injection (10) soit fermée, et l’actionneur (12), à la tension initiale (U$_{0}$), présente une première longueur, et  en ce que  l’actionneur (12) est déchargé de la course de tension prédéfinissable ( Δ U) à la tension cible Revendications 10