Detent escapement

A detent escapement for a timepiece comprising a balance wheel fastened to an impulse element, an escape wheel the teeth whereof intersect the trajectory of the impulse element, a detent swing-arm having a stop element and a disengagement element, means for engaging the stop element in the trajectory of the teeth of the escape wheel, and a disengagement finger, constrained to rotate with the balance wheel, to come into engagement with the disengagement element of the detent swing-arm once per oscillation period of the balance wheel to release the stop element from the teeth of the escape wheel, wherein the disengagement finger is fastened to an inertial member mounted to move freely between two extreme positions in one of which the trajectory of the disengagement finger passes through the disengagement element of the swing-arm and in the other of which this trajectory does not pass through this disengagement element, the passage of the inertial member from one position to the other resulting from the inertia force acting on the inertial member caused by the variations of speed of the balance wheel in each half-cycle of oscillation of the balance wheel.