Patent GB-1251806-A (GB)
IPC: B64C25/46
Filed: 1967-12-06
Abstract: 1,251,806. Brake actuating and anti-skid systems. DUNLOP HOLDINGS Ltd. 4 Dec., 1968 [6 Dec., 1967], No. 55508/67. Heading F2F. A brake actuating system comprises a first mechanism and a second mechanism operable separately to apply an associated brake, an anti-skid means operable to release the brake, and a device for preventing operation of the anti-skid means when the brake is applied by the second mechanism. The separately-operable mechanisms may displace a link member in one direction to apply the brake and the anti-skid means may displace the link member in the opposite direction. As shown in Fig. 1, actuation of the brake pedal serves to admit compressed air at 19 to a "second" chamber 7 to move to the right an annular piston 17 which by means of a sleeve 8 pulls a connecting rod 16 secured directly to the brakes. At the same time a plug 13 threaded into sleeve 8, and a sleeve 28, are pushed to the right by the piston, a valve seating formed on the end of the plug being in contact with a washer 32 so that communication between a "first" chamber 6 and an exhaust chamber 6a (see later) inside the sleeve 28 is interrupted. In these circumstances the brake may be released by admission of compressed air (under control of a skid sensor) at 20 to first chamber 6 where it acts upon a diaphragm 5. A second mechanism for applying the brake includes a hand brake rod 21 connected to a hand brake lever (not shown). Before the hand brake lever is actuated there is a clearance between the head 23 of rod 21 and the inner end of plug 13. When, during actuation, rod 21 is pulled to the right, this clearance is first taken up, in consequence of which a collar on rod 21 pulls washer 32 away from the valve seat on plug 13 against the force of a spring 30. This is the position shown in Fig. 1. Thereafter, plug 13, sleeve 28 and rod 21 are moved to the right together, the valve being continually open. This ensures that the first chamber 6 is in communication with exhaust chamber 6a, which is in communication with the atmosphere through outlet passages 26 past the periphery of the flexible rubber boot 25. In these circumstances, if the anti-skid system fails, tending to leave the chamber 6 pressurized when skid conditions no longer exist, the anti-skid means cannot effect release of the brake because chamber 6 is continuously in communication with the atmosphere. Figs. 2 to 4 (not shown) depict variants of the plug 13-sleeve 28-valve assembly having the same purpose as the one described above. Displacement of the hand brake rod 21 to the right operates a valve (not illustrated) to allow flow of compressed air through a passage 33 to effect servo-assistance by action on the diaphragm 5. In Fig. 5 the brakes (not illustrated) are connected to a rod 62 which is pushed to the right for brake application by each of the two mechanisms. Actuation of the brake pedal serves to admit compressed air at 63 to chamber 59. The brakes may be released by admission of compressed air at 68 to chamber 58 under control of the skid sensor. Actuation of the hand brake lever (not illustrated) serves to admit compressed air at 64 to chamber 61. Chamber 61 is in permanent communication with inlet 72 of a valve device 70 through which normally passes (73 to 74) the air from the source controlled by the skid sensor to the inlet 68 of chamber 58. As soon as chamber 61 is pressurized, valve stem 76 is moved downwards, whereupon the compressed air source and chamber 58 are evacuated to atmosphere at 75 past the now-open valve-andseat assembly 79, 80. Fig. 6 (not shown) depicts an improved form of valve device 70. The valve stem 76 forms, with the casing, a first valve, normally open, between inlet 73 and outlet 74, and a second valve, analogous to that shown in Fig. 5, between outlet 74 and atmosphere at 75. Pressure at inlet 72 then serves to close the first valve and open the second. Hence only chamber 58, and not the compressed air source controlled by the skid sensor, is evacuated to atmosphere, reducing the delay.