Vehicle seat underframe, seat comprising such an underframe and seat assembly comprising such a seat

Vehicle seat underframe comprising:

• a rigid framework intended to be fixed to a seat part of a seat and to be mounted to slide in a longitudinal direction on a horizontal rail fixed to the floor of a vehicle, the framework comprising at least one lower guide shoe which projects downwards and which is intended to engage with a longitudinal guide belonging to the rail, at least one moving catch which comprises a rigid body stretching between an upper end and a lower end, the lower end of the body of the catch being extended laterally by a projecting claw which extends at the level of the guide shoe in a transverse horizontal direction perpendicular to the longitudinal direction, the catch being movable with respect to the rigid framework between at least two positions:
• a locked position in which the claw of the catch projects laterally with respect to the guide shoe in the transverse direction, the claw of the catch then being intended to engage under a rim exhibited by the rail in such a way as thus to prevent the seat from being removed from the rail, the catch being urged elastically towards the locked position, and a retracted position in which the claw is moved towards the guide shoe with respect to the locked position, the claw then being intended no longer to interfere with the rim of the rail and thus to allow the underframe to be removed from the rail, and an operating device designed to move the catch at least between the locked position and the retracted position, the operating device comprising at least one actuating member which is movable between first and second positions corresponding respectively to the locked position and to the retracted position of the catch, wherein the operating device further comprises a release finger constituting a separate part from the catch, the release finger being mounted to pivot with respect to the framework of the underframe about a release finger pivot, the release finger comprising a first branch which extends from the release finger pivot as far as a free end and a second branch which extends from the release finger pivot as far as a free end, the release finger being movable between:
• an effaced position in which the second branch of the release finger is designed to be raised enough for the second branch not to interfere appreciably with the rail on which the underframe is intended to be mounted, and an active position in which the free end of the second branch projects downwards from the framework of the underframe so that when the guide shoe of the underframe is engaged with the longitudinal guide of the rail, the rail lifts the free end of the second branch of the release finger and returns the release finger to the effaced position, the release finger being urged elastically towards the active position, wherein when the release finger is in the effaced position, the first branch of the release finger is designed to bear against a cam surface belonging to a release cam connected to the actuating member, as long as the actuating member is not in the second position, then holding the release finger in the effaced position, and wherein the release finger is designed so that when the release finger is in the active position, the free end of the first branch of the release finger comes into abutment against an abutment face integral with the release cam, thus holding the actuating member of the operating device in the second position.