Patent GB-1409937-A (GB)
Title: Braking system having automatic brake wear adjustment
IPC: F16D65/18
Filed: 1973-11-26
Abstract: 1409937 Hydraulic full-face disc brakes; wear adjusting; two piston actuators GOODYEAR TIRE & RUBBER CO 26 Nov 1973 [27 Dec 1972] 54711/73 Headings F2E and F2F A brake system associated with a housing and the pressure plate of a stack of brake discs comprises a telescopic fluid-pressure-actuated piston sub assembly part of which is fixed to the housing and part in operative engagement with the pressure plate and a telescopic return mechanism part of which is attached to the housing and part in operative engagement with the pressure plate, so that upon release of actuation of the piston subassembly the return mechanism acts to relieve the frictional engagement of the discs of the stack, the application and release operations being unaffected by wear of the brake discs. Preferably the system is applied to an aircraft wheel having carbon brake discs. Fig. 1 shows a telescopic-piston hydraulic actuating means having a fixed sleeve 12, a larger piston 16 prevented from leaving the sleeve by engageable annular shoulders 34, 32, and a smaller piston 14 similarly prevented from leaving the larger piston 16. The pistons are urged apart by springs 18, 20, 22 of which spring 22 also acts upon a valve member 24 engageable with a seat 52 in piston 16; piston 14 is secured to an annular pressure plate 46 beyond which are located the discs of the stack (not shown). In the off-position of the brake, contact pin 30 of valve member 24 is in engagement with a fixed part of the brake structure so ball 28 is out of engagement with seat 52 (not as shown). Thus, in operation, hydraulic fluid admitted to sleeve 12 acts on the left-hand end of piston 16 but initially also flows past open valve 24, 52 into cavity 56 and acts directly on piston 14 which alone moves until all the discs of the stack are in engagement, whereupon movement of piston 14 ceases. As hydraulic pressure increases, piston 16 is forced to the right, overcoming the force of springs 18, 20, while valve member 24 is held stationary by spring 22. When seat 52 reaches ball 28, pistons 14, 16 move in unison, applying braking pressure to the stack. During brake operation, spring 62, Fig. 2, of a telescopic return mechanism is compressed, and when hydraulic pressure is relieved for brake release, spring 62 acting through spring follower 64, sleeve 66, tubular member 68 and bolt 72 draws pressure plate 46 to the left. Tubular member 68, Fig. 3, and sleeve 66, Fig. 5, are shown the wrong way round compared with their orientations in Fig. 2. In addition to the screwthreads 76, 88 and 82, an external screwthread 80 is provided on sleeve 66, but none of the screwthreads is used as such, mutual rotation being prevented by wires located in grooves 81, 85 respectively, Fig. 5A. Wear adjustment during brake operation occurs as follows. When during brake application spring 62 is fully compressed before pressure plate 46 has effected engagement of all stack discs, fluid pressure acting on plate 46 and therefore on bolt 72 causes tubular member 68, whose threads 76 are in engagement with some of threads 82, and which is rendered resilient by cross cuts 78, to jump one thread of 82. As wear continues, this process continues until head 74 is retained by groove 86. Thereafter, sleeve 66 jumps one thread of 88 at a time until its head 84 is retained by shoulder 94. In the complete brake, several devices of Fig. 1 and several mechanisms of Fig. 2 alternate into a circular array.