Hydromechanical clutches with a differential driving gear can protect against sudden quickly growing shortterm overloads not related to emergency without triggering at the expense of a smooth moment increase on a shaft of the engine provided with the operation of hydroelastic elements in the hydrosystem of a clutch. The investigation of the friction influence in ki-nematic pairs of hydromechanical clutches with helical and toothed differential driving gears upon the dynamics of clutch operation during emergency triggering has shown that in a helical driving gear the kinetic friction in a spline connection and in a pair of “screw-nut” increases a moment on a shaft of an electric motor overloading it longer than it is admissible. It means, that such a type of clutches may be used only as elastic-damping one decreasing the dynamics of the whole dynamic system at the expense of high friction in kinematic pairs, or jointly with the protection on current as a smooth increase of a moment on a shaft of the electric motor even at the overload increasing in spurts ensured by a clutch increases protection efficiency on current. In the toothed driving gear friction in kinetic pairs is low and a driving gear does not actually experience an overload that means high efficiency of driving gear protection against rapidly growing random overloads with such a type of clutches.