Hydraulic Clutch Control System, Comprising Servo Means Which Are Disposed Between The Master Cylinder And The Slave Cylinder Of The System

Hydraulic control system (10) for a clutch (12) for a motor vehicle, comprising an upstream sending cylinder (14) connected by a conduit (16) to a downstream receiving cylinder (18), so as to form a hydraulic control circuit (19), an assistance cylinder (30) that is interposed in the conduit (16), between the sending cylinder (14) and the receiving cylinder (18), and which comprises at least one assistance piston (32) that is mounted so as to slide axially (A1) in the body (56) of the assistance cylinder (30) between an upstream engagement position and a downstream disengagement position, so as to delimit an upstream hydraulic chamber (34) and a downstream hydraulic chamber (36) with variable volumes according to the axial position of the piston (32), the upstream chamber (34) being connected to the sending cylinder (14) by a portion of hydraulic circuit referred to the upstream circuit (40) and the downstream chamber (36) being connected to the receiving cylinder (18) by a portion of the hydraulic circuit referred to as the downstream circuit (44), each hydraulic circuit portion (40, 44) comprising a means (52, 102, 150) of relevelling the volume of fluid connected to at least one fluid reservoir (29), and in that the assistance cylinder (30) comprises an assistance device (50) that applies an assistance force (Fa) to the assistance piston (32) during the declutching phase.