Hydraulic clutch control system, comprising servo means which are disposed between the master cylinder and the slave cylinder of the system

A 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) interposed in the conduit (16), between the upstream sending cylinder (14) and the downstream receiving cylinder (18);
• and
• at least one assistance piston (32) mounted so as to slide axially along a sliding axis (A1) in a 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 assistance piston (32);
• the upstream chamber (34) being connected to the upstream sending cylinder (14) by a portion of hydraulic circuit referred to as an upstream circuit (40) and the downstream hydraulic chamber (36) being connected to the downstream receiving cylinder (18) by a portion of the hydraulic circuit referred to as a 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);
• the assistance cylinder (30) comprising an assistance device (50) disposed in the cylinder body (56) for applying an assistance force (Fa) to the assistance piston (32) during a disengagement phase of the clutch (12);
• the assistance device (50) comprising a regulation means (114, 115) varying the value of the assistance force (Fa) according to the travel (CP) of a clutch control pedal (22) in accordance with a predetermined assistance law, and an elastic element (106) for storing energy during an engagement phase of the clutch (12) and for restoring the energy during the disengagement phase in order to produce the assistance force (Fa);
• the regulation means (115) being a cam mechanism (114) driven by the axial movement of the piston (32) for regulating the assistance force (Fa) produced by the elastic assistance element (106) during the disengagement phase;
• the cam mechanism (114) comprising at least one control surface (120, 122) produced on an internal wall of the cylinder body (56);
• the elastic assistance element (106) being an axial compression elastic element interposed axially between a cup (108) and an abutment surface (110) fixed with respect to the assistance cylinder body (56),
• the cam mechanism (114) comprising at least one movable roller (116, 118) which travels over the control surface (120, 122) between an upstream position and a downstream position corresponding respectively to the upstream and downstream positions of the assistance piston (32);
• the movable roller (116, 118) connected by a first connecting rod (124) to the piston (32) by a second connecting rod (126) to the cup (108);
• the axis by which the connecting rods (124, 126) pivot on the movable roller (116, 118) being concurrent with a rotation axis (A2) of the roller (116, 118);
• the control surface (120, 122) comprising an upstream portion (134) inclined with respect to the sliding axis (A1) and a downstream portion (136) substantially parallel to the sliding axis (A1) so that, during a first part of the disengagement phase, the movable roller (116, 118) moving first of all on the inclined portion (134) towards the sliding axis (A1) and in the downstream direction, from the upstream position thereof, transmitting part of the relaxation force of the elastic assistance element (106) to the assistance piston (32), by a step-down effect, and then, during a second part of the disengagement phase, the movable roller (116, 118) moving on the downstream portion (136) in the downstream direction, in the substantially axial direction, transmitting all the relaxation force of the elastic assistance element (106) to the assistance piston (32);
• the distance between the pivot axes of the second connecting rod (126) being such that, in the upstream position of the movable roller (116, 118), the roller moving in the upstream direction beyond a point (B1) on the control surface (120, 122) where the second connecting rod (126) being perpendicular to the control surface (120, 122), so that the expansion force of the elastic assistance element (106) biasing the movement roller (116, 118) towards its upstream position;
• the axial dimension of the elastic assistance element (106) in the relaxed state being less than the axial distance between the cup (108) and the associated fixed abutment surface (110), when the piston (32) occupies its downstream position, so as to eliminate the assistance force (Fa) during the end of the travel of the piston (32) in the downstream direction.