Patent GB-1142853-A (GB)
Title: Improvements in boosters for use in hydraulic systems
Inventor: YARDLEY ALFRED
IPC: B60T13/24
Filed: 1965-04-27
Abstract: 1,142,853. Fluid-pressure brakes. GIRLING Ltd. 26 April, 1966 [27 April, 1965; 30 July, 1965], Nos. 17647/65 and 32665/65. Heading F2F. In a booster arrangement for an hydraulic braking system including an auxiliary cylinder and a vacuum booster which is controlled by hydraulic pressure supplied behind a piston of the auxiliary cylinder by a pedal-operated master cylinder to control a valve, e.g. a rocking valve, such as that described in Specification 786,524, which controls the pressure differential across a power piston of the booster, initial displacement of the auxiliary piston by the power piston, which acts via a rod, is arranged to take place either before or after closure of a path bypassing the auxiliary piston for recuperation purposes, the auxiliary piston being free to move forwardly away from the rod. In the embodiment of Fig. 3, the auxiliary piston is composed of two telescoping portions 17a, 17b normally held in the positions shown by return spring 42, which maintains portion 17a normally in contact with the rod 13, and a light spring 59. In this relative position the forward end of portion 17b maintains a ball 91 off a seating formed in a transverse bore 90 of the portion 17a, so that the fluid can pass freely in either direction between the space 14 behind the auxiliary piston and the pressure space 16 in front of the auxiliary piston, which is connected to the brakes. When the booster has been energized, its power piston moves the rod 13 forwardly while the spring 59 maintains a flange 17c of the portion 17b in abutment with a stop 40. As a result, the ball 91 no longer contacts the forward end of the portion 17b and closes the bore 90. Such closing of the by-pass after initial displacement of the auxiliary piston is said to reduce or eliminate " hydraulic knock." Smoothness of operation is also ensured by the provision of a second bore 54 in the front face of the auxiliary piston, normally closed by a conical end of the rod 13 engaging a conical seating behind the bore, sudden application of the brake causing the auxiliary piston to move forwardly away from the rod to open this second bore. In a second embodiment, Fig. 4, the auxiliary piston again comprises two portions 17a, 17b urged apart by a spring 59, but the ball valve is replaced by an annular passage 62 which is closed by shoulder 60 of the rod 13 when this has advanced sufficiently, there being a bore 68 drilled axially through the front face of the auxiliary piston to complete the by-pass. A second bore 54, normally closed by the end of rod 13, is also provided as previously. In a third embodiment, Fig. 5, the rod 13 is hollow and contains a spring 69, the forward end of which projects sufficiently to act as a cushion against the face portion 63 of the auxiliary piston which in this embodiment consists of a single member. Only one by-pass is provided, consisting of the bore 54 and transverse bores 68 in the rod 13. The latter are closed off after a forward movement of the rod 13 sufficient to carry them past a seal 70. Two further variations are also described (Fig. 7, not shown) which are similar to the embodiment of Fig. 5 excepting that the transverse bores (68) are in this case located nearer the end of the rod (13), which projects beyond the front face of the piston after the rod has moved forward to close the by-pass, the by-pass being formed by an annular passage (76) within the piston, the bores (68) and the hollow end of the rod (13), and closure of the by-pass being effected by movement of the bores (68) past a seal (74) which is located in a recess at the front of the piston. The spring 69 is omitted and is replaced by a spring (77) arranged within a recess at the rear of the piston.