GB1115892A - Improvements in power assisting mechanisms - Google Patents

Abstract

1,115,892. Fluid-pressure brakes. ROBERT BOSCH G.m.b.H. 30 July, 1965 [1 Aug., 1964], No. 32599/65. Heading F2F. A fluid-pressure brake servomotor, particularly of the vacuum-suspended type, has a follow-up type valve, the pedal-operated element of which comprises a sleeve 11 which is guided both in a plastic bush 21, retained by a seal 23 and ring 24 within a short neck 22 formed on the front end 2 of the cylinder 1, and in a guide plate 20 welded to the piston 3 of the servomotor, and a valve closure member 30, guided on a rod 8 within the sleeve 11, is urged by a spring 33 against one or other of two valve seats 31, 32 carried by the sleeve and piston, respectively, according to the relative positions of the sleeve and piston during brake operation, as determined by the pedal and reaction forces. The latter are communicated to the sleeve 11 via a plurality (three, as shown) of levers 4 arranged radially with their mid-portions engaging a rib 49 of the output member, which comprises a plate 5 and a rod 6, their outer ends engaging a rib 48 of the piston and being apertured to receive studs 50 secured to the piston, and their inner ends engaging a collar 7 on the rod 8. The latter has a socket and flange 9, at its forward end, this, together with another socket element 12, enclosing a ball 15 on the rear end of a pedal-operated rod 16, and being located against a shoulder 10 of the sleeve by a sleeve 13 and circlip 14. Springs 51 surrounding the studs 50 act between pins 53 carried by the studs and the plate 5, so that in the inoperative position levers 4 urge the sleeve 11 to a forward position determined by engagement of a stop ring 26 with the guide plate 20, in which position vacuum connected at 43 to the forward chamber is also communicated to the space behind the piston 3. When the pedal is operated, sleeve 11 moves rearwardly so that closure member 30 engages seat 32, and seat 31 then leaves the closure member to admit air via apertures 41, 42 to the space behind the piston to operate the servomotor, reaction forces acting through the levers subsequently determining a lap position of the valve. As the sleeve follows up piston movement, the two bearing surfaces provided by bush 21 and plate 20 become further apart so that the reaction forces are adequately sustained in spite of the short guide surfaces these members provide.