The present invention relates generally to torsion damping assemblies, namely for motor vehicles, of the type comprising two coaxial members, that is, a hub and a radially extending web disposed annularly around the hub, which are rotatably mounted with respect to each other against the force of resilient centering means, for predetermined relative angular displacement within limits defined by meshing means provided between said members, one of the members having at least one meshing member such as a tooth or a notch intermeshing with circumferential play with a complementary meshing member, such as a notch or a tooth, disposed on the other member facing the first meshing member.
In practice when such a torsion damping assembly is employed in a friction clutch assembly for a motor vehicle, the coaxial members together form a first part with which a second part is coaxially associated; the second part is rotatably mounted relative to the first part for predetermined relative angular displacement against the force exerted by circumferentially disposed resilient return means interposed between the parts and also carries a friction plate.
Such a torsion damping assembly inserted in a kinematic chain from an input shaft to an output shaft, enables a controlled transmission from one of the coaxial component parts to the other of torque which may be applied to one of the parts, that is, sufficient to regulate the angular velocity of the input shaft and thereby diminish the acceleration of the output shaft in order to prevent vibrations, particularly audible vibrations, which occur anywhere along the kinematic chain on which it is located.
More specifically, for small relative angular displacements between the component parts of such an assembly, the torque transmitted therebetween remains, advantageously, small as long as the meshing means provided between the component members of the first part, as briefly set forth above, do not cause one of the members to be positively driven by the other.
This assembly is adapted, for certain particular uses, namely motor vehicles, to prevent generating various noises, such as a gear box noise, or dead point noise, due to impacts produced between the teeth of gears of the gear box when it is in neutral, owing to periodic oscillations in the angular velocity of the engine inherent in the mode of operation of internal combustion engines.
Thus for small angular clearance or play between two component parts of such an assembly only the two component members of the first part vary in relative angular position, the second part being fixed circumferentially to the web constituting one of the members by circumferentially disposed resilient means interposed between the parts, which resilient means are stiffer than resilient means effecting the centering of the members relative to each other.
It is, moreover, known to insert between the two coaxial parts making up such a torsion damping assembly friction means adapted to introduce a "hysteresis" effect which results in a difference for a given relative angular displacement between the parts between the torque transmitted in a first direction of rotation, usually termed the forward direction, and the torque transmitted in the opposite direction, termed the reverse direction.
It has been established that for certain uses the hysteresis effect contributes to limiting the relative amplitude of oscillations of the rotatable parts concerned.
It is also known to provide friction means generating such a hysteresis effect by means of friction washers of which at least one is maintained axially in contact with the web forming one of the rotatable members of the torsion damping assembly.
Yet to the present day such friction washers are ineffective for small amplitude oscillations for which only the relative angular position of the coaxial members varies relative to each other, which coaxial members comprise the first of two component parts of the assembly.
Indeed, as pointed out above, for the small amplitude oscillations in question the second component part of such an assembly is fixed for rotation with the web which is part of the first part so that the friction washer(s) in contact with this web is not subjected to any rotational movement relative to the same and therefore does not develop any friction in contact therewith.
Now, when the oscillations of the torsion damping assembly are greater, the meshing means provided between the members forming the first of the component parts of the assembly positively drive the members relative to each other and the circumferentially disposed resilient means interposed between the parts come into action, there may be produced, taking account of the substantial stiffness of the resilient means relative to the stiffness of the resilient means reduced by the resilient centering means interposed between the members, an accidental rebounding of one of the members relative to the other part to interfere with the uniformity of the desired speed of output shaft which is usually the input shaft of the gear box and therefore liable to adversely affect sought after noise reduction.