via a connecting line 28 in which is arranged a hydraulically deblockable switchover valve 29 having spring resetting fluid connection 122 b of second working chamber 122 of valve actuator 11 b is likewise connected via a check valve 30 to the intake of second electric control valve 26 switchover valve 29 has a hydraulic control input 291 that is connected via a control line 31 to the outlet of a further switchover valve 32 able to be actuated electromagnetically on the intake side further switchover valve 32 is connected via a check valve 33 to second working chamber 122 of valve actuator 11 a alternatively however the intake side of further switchover valve 32 may also be connected to output 201 of pressure supply device 20 or to a low pressure circuit of the internal combustion engine the outlet side of further switchover valve 32 is connected via corresponding control lines 31 to all control inputs 291 of switchover valves 29 for all valve actuator pairs if as in the exemplary embodiment of fig1 switchover valve 32 is constructed as a 2 2 way solenoid valve with spring resetting then for the relief of control line 31 a discharge valve 35 formed as a 2.