A flywheel module 3 comprises a bypass transmission P that has three rotational members, and a flywheel F that is connected to a first one of the rotational members r1. A second one of the rotational members r2 is connected to the input/output 9. The flywheel module further includes an electric machine MG which can function both as a motor and as a generator and which is connected to a third one of the rotational members r3, as well as actuation means formed by a battery A for actuating the electric machine. The flywheel module further includes a control unit for driving the actuation means, as well as operating means for operating the brake and the clutch. These operating means comprise no more than a single actuator for operating both the clutch and the brake. The actuator is connected to the clutch and the brake such that the actuator either opens the clutch and closes the brake or vice versa.