GB1490605A - Vehicle braking systems - Google Patents

Abstract

1490605 Hydraulic brake booster systems DAIMLER-BENZ AG 23 Oct 1975 [30 Oct 1974] 43650/75 Heading F2F On failure of a booster 3 the transmission ratio is reduced of an associated device between a pedal and a master cylinder 6 and comprising a pressure medium chamber 22, an input piston 21 and an output piston the effective diameter of which is increased by operation of a switch controlled retainer. The device (1, la) may be on either side of the booster 3 (Figs. 1a, 1b, not shown). In one construction, Fig. 2a, movement of an input piston 21 normally displaces a piston 19 within an outer piston 20 but on booster pressure failure a solenoid lifts a retainer 14 when the pistons 19, 20 move together at a slower rate. The pistons 19, 20 may be co-axial or spaced apart radially of one another. In a second construction, Fig. 3c, the outlet piston 28 is a master cylinder piston and has a bore 36 containing a piston 37 communicating with a reservoir through an annular passage (35), a port 29 and a one-way valve 32. Normally the piston 37 is at the outer end of the bore 36 and the valve 32 is closed preventing escape of fluid from the bore 36. When the input piston 34 is moved into the chamber 38 its extension contacts the piston 37 which it moves together with the piston 28. Further fluid enters the enlarging chamber 38 through a port 41 and past the one-way seal 42 on the piston 34. On brake release, fluid escapes from the chamber 38 through a further one-way valve 33. On booster power failure solenoid actuated retainers 44 open the valve 32 and close the valve 33. On movement of the piston 34 the piston 37 moves to the bottom of the bore 36 due to its smaller area than the piston 34 after which the piston 28 is moved at a slower rate than the piston 34 due to its greater area until the piston extension comtacts the piston 37.