is great then a higher force is required the magnetic force required to open the metering valve 24 can be characterized in turn according to one exemplary embodiment via the profile of the current i_dv of the metering valve activation signal 34 which is shown in more detail in fig2 over time the effects of the difference in force are evident upon opening of the metering valve 24 starting from the start time t 0 of the metering valve activation signal 34 as far as the time t 1 after the current rise 40 which may be for example within the range of 1 a 200 u03bcs a current maximum ip_dv which may be for example at 1 a is reached at the first time t 1 and then a current drop 42 occurs the current drop 42 is caused by the change in the inductance of the magnetic circuit which comprises the armature 28 with the valve needle 30 as well as the coil 36 during the opening operation of the solenoid valve 24 after the current dip a holding current which preferably lies below the current maximum ip_dv can be set the reaching of the current maximum ip_dv at the first time t 1 can be approximately equated with the opening of the metering valve 24 the first time t 1 can be determined for example.