Such a lock-up clutch is known from French patent specification No. FR 2 726 620A, in which the said two elements are secured together in rotation through tongues, the lengthwise dimension of each tongue extending substantially along a chord of a circumference of the assembly, with first ends of the tongues being connected to a first one of the said two elements, through a driving or attachment ring common to all of the tongues, the attachment ring being attached to the said first element.
The tongues are mounted in the control chamber, and the second end of each tongue is attached to the second one of the said elements by a corresponding one of a plurality of fastening means, each fastening means comprising a first part applied to the second end of the corresponding tongue and comprising a head which is extended axially by a fastening shank that extends through a corresponding through hole in the second end of the tongue, so that the shank extends axially beyond a lateral face of the tongue (referred to as an internal face), which is gripped axially against a lateral engagement face (referred to as an external lateral engagement face) which is formed in facing relationship on the said second element.
The fastening means proposed in the above mentioned French patent specification include, on the other side of the second element, a second part which engages with the first part. These fastening means which are employed for attaching the tongues to the piston, which in that French patent constitutes the second element, enable assembly to be carried out blind, and with a reduced number of components, by a simple process of stacking the components in a common axial direction. First of all the piston is engaged on the first parts of the fastening means carried by the second ends of the tongues, and subsequently the second parts of the fastening means are very simply put in place. In order to engage the second parts with the associated first parts of the fastening means, it is only necessary to work on one side of the piston.
In order to permit these assembly and fastening operations, it is however necessary to provide a radial clearance between the body of each shank of a first part of the fastening means and the axially oriented hole of the piston through which it extends. The simple effect of axial seaming or gripping that results from the engagement of the second parts on the first parts does not allow for any fortuitous subsequent displacements of the piston that may occur with respect to the shanks in a radial plane, which can be detrimental.
In general terms, each fastening means include at least one first part having a head which is extended axially by a fastening shank applied to the second end of the corresponding tongue, with the fastening shank passing with a radial clearance through the said second element of the clutch, so as to facilitate fitting of the second element on the shanks or fitting of the shanks on the second element.
It is therefore important to avoid any possible displacement of the second element with respect to the shanks, and to do this in a simple and inexpensive way.