hydraulic actuator is exposed to nor do production tolerances of the actuator affect this position as a result of the suitable choice of the diameters d 1 through d 6 the ratios of the opening force upon liftoff of the gas exchange valve from the valve seat and the reduced opening force upon further opening of the gas exchange valve and the closing force upon closure of the gas exchange valve can be adapted to one another in order to attain an optimal operating performance of the hydraulic actuator in fig3 the actuator of fig1 is shown in fragmentary form only to the extent of interest below with the housing 1 first chamber 13 second chamber 27 and third chamber 25 and with its hydraulic connection to the hydraulic pump 31 with the first switching valve 29 embodied for instance as a 2 2 way magnet valve and the hydraulic communication between the first chamber 13 and second chamber 27 via the throttle 49 the hydraulic relief chamber or oil sump is identified as before by reference numeral 35 and the line connecting the second chamber 27 with the second switching valve 33 embodied for instance as a 2 2 way magnet valve is identified by reference numeral 37 the hydraulic actuator has been modified to the extent that the device for limiting the volumetric decrease of the second chamber 27 which in fig1 is embodied as a hydraulic spring reservoir 41 is now replaced with a shutoff valve 50 which is in communication with an opening in the second chamber 27 for instance being connected to the line 37 and in one switching position it.