| 摘要 |
<p>The invention concerns a motor vehicle braking device comprising a master cylinder (2), a primary piston (3) mounted sliding in the master cylinder, a manual control member (4), a brake servo unit coupled with the manual control member, an emergency power valve (VA) comprising a reaction piston (17a) and a fast piston (17b), and a ratio control unit (T) actuated by a distributor plunger (10) driven by the control member (4). The reaction piston (17a) and the fast piston (17b) form a single and common staged piston (17) having a large section portion (17a) and small section portion (17b), the large part section (17a) defining with a bore (18) of the primary piston (3) a variable volume annular chamber (27). Separating/communicating means (28, 29, 30), controlled by the displacement of the staged piston (17), are provided so that the liquid pressure is efficiently applied on the large section (17a) of the staged piston when the latter takes up its neutral position or is rearward of said position, and only on the small section (17b) when the staged piston has moved forward relative to the main piston during emergency braking.</p> |
