A COPY VALVE FOR AN ANTI-LOCK BRAKE SYSTEM

A copy valve (10) for an anti-lock brake system. The copy valve (10) has a housing (110, 172) enclosing four chambers (114, 116, 112, 118; 188, 202, 190, 196). A first (114, 188) and fourth (118, 196) chamber of the enclosed four chambers receives pressurized fluid directly from the first and second cylinders of a dual master brake cylinder (18). The third chamber (112, 190) receives the pressure of the (electronically) controlled brake actuator (28) while the second chamber (116) is connected to the uncontrolled brake actuator (36). In one embodiment, a single piston (178) is enclosed in the housing (172) and the first (188) and second (202) chambers are disposed at the opposite ends of the piston (178). The piston (178) has an enlarged collar (179) intermediate the two ends which is received in an annular recess (177) provided in the housing (172). The third chamber (190) is formed between a first face (194) of the piston's enlarged collar (179) and the annular recess (177) while the fourth chamber (196) is formed between the opposite face (198) of the piston's enlarged collar (179) and the adjacent face (200) of the housing (172). A throughbore (214) is provided through the piston (178) connecting the first (188) and second (202) chambers. A valve (218, 220) disposed in the throughbore (214) is open when the piston is in the second chamber (202) and closed when the piston is displaced from the second chamber (202). In another embodiment, the copy valve (10) comprises two separate pistons (140, 150) each interacting with a valve element (146; 158, 162). Soupape reproductrice (10) pour système de freinage antiblocage comprenant un boîtier (110, 172) qui renferme quatre chambres (114, 116, 112, 118, 188, 202, 190, 196). La première (114, 188) et la quatrième de ces chambres reçoivent le fluide sous pression directement du premier et du deuxième cylindre du maître cylindre de frein (18) à deux chambres. La troisième (112, 190), reçoit la pression de la commande (28) de freinage à contrôle électronique tandis que la seconde (116), est reliée à une commande de frein sans contrôle électronique. Dans l'une des variantes, le boîtier (172) ne renferme qu'un piston (178) et la première et la seconde chambres (188, 202) sont prévues aux extrémités opposées du piston (178). Ledit piston (178) présente entre ses extrémités un renflement circulaire (179) qui vient se placer dans un évidement annulaire (177) pratiqué dans le boîtier (172). La troisième chambre (190) se