A Novel Double-Sided Electromagnetic Dog Clutch with Integrated Synchronizer Function

Dog clutches are superior to synchromesh units due to much less wear caused by friction, but require an external torque source to synchronize the rotation speeds. The current trend in e-mobility to use the driving motor of an electric vehicle as this source just creates another problem, which is known as torque holes. In this work, we propose a novel double-sided dog clutch that synchronizes the speeds electromagnetically by itself avoiding a mechanical contact between the parts. A shift sleeve, two coils placed coaxially in their stators and two complementary rings form an electromagnetic reluctance actuator, which is integrated inside the gearbox between two gearwheels and represents the double-sided clutch. Thus, intermediate parts between the shift sleeve and the actuator are not required. Both actuator sides can produce axial force to engage the shift sleeve and electromagnetic torque to synchronize the speeds. However, torques and forces are generated simultaneously on each side, therefore, a special control algorithm is developed to keep the resulting axial force approximately equal to zero while the torque is generated in neutral gear position. After the synchronization, the axial force is applied on the corresponding side to shift the required gear engaging the shift sleeve teeth directly with the slots of the complementary ring mounted on the gearwheel. So, an axial contact of the teeth at unaligned state, which can lead to unsuccessful shifting, is avoided. A clutch prototype and a testing two-speed gearbox were designed and built. The developed theoretical ideas were completely verified during the experiments. Both gears could be shifted with a preliminary contactless reduction of the speed difference and a subsequent direct engagement of the shift sleeve. The experiments were successful both at positive and negative initial relative speeds.