A combination cylinder containing a service brake cylinder as an active service brake having at least one pressure-medium-actuated service brake piston, which actuates a brake mechanism via a service brake piston rod, and also containing a spring brake cylinder as a passive parking brake having a spring brake piston actuated by pressure medium counter to the action of at least one accumulator spring, wherein the spring brake piston transmits the force of the at least one accumulator spring to the service brake piston rod in the parking braking situation, characterised in that a) the parking brake force generated by the spring brake piston can be introduced into a rotationally fixedly mounted thrust ring, which can be actuated coaxially with respect to a central axis of the combination cylinder and which exerts axial forces on a spindle drive (46, 50; 100, 102), and an axial force transmission is provided between the spindle drive (46, 50; 100, 102) and the service brake piston rod, wherein b) one part (50; 102) of the spindle drive (46, 50; 100, 102) is mounted in a rotationally fixed manner and another part (46; 100) of the spindle drive (46, 50; 100, 102) is rotatably mounted coaxially with respect to a central axis of the combination cylinder, wherein it is possible for the rotational movement of the rotatable part (46; 100) of the spindle drive (46, 50; 100, 102) to be blocked by means of a releasable rotational lock for axial force transmission between the rotationally fixed part (50; 102) and the rotatable part (46; 100) and to be unblocked in order to eliminate said axial force transmission, and wherein c) the rotational lock contains a pawl, which can engage in an external toothing of the rotatable part (46; 100) of the spindle drive (46, 50; 100, 102) and which is rotatably mounted on the thrust ring, and the releasable rotational lock is part of an emergency release device for the emergency release of the parking brake, and d) the releasable rotational lock is blocked in normal operation and is released for the emergency release of the parking brake. a) the parking brake force generated by the spring brake piston can be introduced into a rotationally fixedly mounted thrust ring, which can be actuated coaxially with respect to a central axis of the combination cylinder and which exerts axial forces on a spindle drive (46, 50; 100, 102), and an axial force transmission is provided between the spindle drive (46, 50; 100, 102) and the service brake piston rod, wherein b) one part (50; 102) of the spindle drive (46, 50; 100, 102) is mounted in a rotationally fixed manner and another part (46; 100) of the spindle drive (46, 50; 100, 102) is rotatably mounted coaxially with respect to a central axis of the combination cylinder, wherein it is possible for the rotational movement of the rotatable part (46; 100) of the spindle drive (46, 50; 100, 102) to be blocked by means of a releasable rotational lock for axial force transmission between the rotationally fixed part (50; 102) and the rotatable part (46; 100) and to be unblocked in order to eliminate said axial force transmission, and wherein c) the rotational lock contains a pawl, which can engage in an external toothing of the rotatable part (46; 100) of the spindle drive (46, 50; 100, 102) and which is rotatably mounted on the thrust ring, and the releasable rotational lock is part of an emergency release device for the emergency release of the parking brake, and d) the releasable rotational lock is blocked in normal operation and is released for the emergency release of the parking brake.