Losses in conventional automotive and hybrid powertrains can be reduced on both the engine and the transmission side. On the engine side for instance, cylinder deactivation can reduce the fuel consumption of an internal combustion engine (ICE). Friction losses of the non-firing cylinders still remain. Therefore, ICEs which are mechanically divided into two individual engines promise an even higher potential in terms of fuel economy. The objective of this paper is to present the concept of a clutch unit that is able to connect two ICEs. Thus, it is possible to create an innovative, cost- and fuel-efficient powertrain architecture for automotive applications: This is the concept of the Split-Crankshaft Engine (SCE). In a first step, this powertrain architecture and its particular requirements will be discussed. In a second step, a selection of proposals for crankshaft connecting clutches that have been presented in recent years will be detailed. The clutch concept of the SCE will be depicted in a third step: a switchable, electromechanically actuated clutch unit for load-dependent activation of the secondary engine. In order to reduce costs and weight as well as to minimize activation durations, the secondary engine will be started through a friction clutch. When the two sub-motors are synchronized, a form-locking, second clutch will be engaged in order to ensure the connection of both engines at high torque.