1. Field of the Invention
The present invention relates to a mechanical timepiece comprising an oscillator, the oscillating motion of which is maintained by a mainspring, in which a periodic energy storage device is disposed between this mainspring and an escapement associated with said oscillator.
2. Description of Related Art
The energy source for said mechanical timepieces is constituted by a mainspring constituted by a leaf spring wound in a barrel, its outer end being fixedly connected to the barrel drum, whereas its inner end is fixedly connected to the arbor of this barrel. Upon slackening, the mainspring drives the barrel drum. The latter has an external toothing engaging with the train of the timepiece, which toothing ends at the escapement intended to transmit the force of the mainspring to the regulator. With each turn of the hairspring, the latter trips a tooth of the escapement wheel, which, under the pressure exerted upon the train by the barrel spring, transmits to it an impulse serving to maintain the oscillation of the hairspring.
The force exerted by this mainspring upon the train is clearly not the same when this spring is fully wound or at the end of its winding. Consequently, the force transmitted by the escapement to the hairspring is not constant and the amplitude of the balance wheel varies, affecting its isochronism. Its period of oscillation will be shorter when the force is greater, whereas it will lengthen once this force diminishes.
Indeed, it has already been proposed to store energy temporarily between the barrel and the escapement in order to deliver a constant energy to the regulator system. The known devices to this effect can no longer be operated once the spring has been fully unwound, such that means have to be provided to stop the timepiece prior to complete unwinding of the mainspring so as to allow restarting of this timepiece after it has been rewound.
Moreover, these devices are not designed to be able to be housed in a watch, especially in a wrist watch, but are rather intended for clocks in which the problem of bulk does not have the same importance as in watches and particularly in wrist watches.