GB1239040A - - Google Patents

Abstract

1,239,040. Dual hydraulic circuit wheel cylinders; spot-type disc brakes; cooling. SOC. ANON. FRANCAISE DU FERODO. 23 Oct., 1968 [24 Oct., 1967], No. 50288/68. Headings F2E and F2F. A twin circuit wheel cylinder has two telescoping pistons, both pistons however engaging in the single bore of the cylinder with some part of their periphery, the assembly defining two chambers, each connected to one of the two circuits; one chamber is central, is formed between central end faces of the two pistons, and is fed through an external piston-face, while the other chamber is peripheral, is formed between peripheral end faces of the two pistons, and is fed through the cylinder casing. As shown in Fig. 2, the first of the pistons, 3, is socket-shaped, forming a blind recess with a base 5, and the second piston, 4, has a shoulder 7 followed by a shank 8 which is engaged in the blind recess, the central chamber 13 being provided between the base 5 of the blind recess and the base 14 of the second piston 4, and the peripheral chamber 17 being provided in the annular gap between the shared cylinder bore 2, the lateral surface of the shank 8, and shoulder 7 and annular surface 6. Preferably, as shown, the second piston 4 is hollow and provides a body of insulating air between the hydraulic section and a frictionally-heated part (see below). The circuit connected to the central chamber 13 includes a passage 15 provided in the first piston 3, while the circuit connected to the peripheral chamber 17 includes a passage, shown dotted, provided in the cylinder 2. As applied to a spot-type disc brake, piston 4 is secured directly to a friction lining, while piston 3 is secured to a collar 26 connected to the friction lining on the other side of the rotary disc being braked. Only three seals are necessary- 10, 11, each of square section and accommodated in grooves of smaller trapezoidal section, and 12, of toroidal or double-lip type. Fig. 5 shows an embodiment orientated the opposite way round to Fig. 2. The first piston 3<SP>1</SP> is secured directly to the friction lining 23 and is not provided with a passage supplying fluid to the central chamber 13: instead, the second piston 41 is provided with the passage 15, and the base 31 of the second piston is provided at the end remote from the shank 8. In both embodiments, the cylinder is fixed. It is stated that the invention may be applied to a drum brake.