GB728251A - Improvements in or relating to disc brakes for vehicles - Google Patents

Abstract

728,251. Disc brakes. GIRLING, Ltd. March 18, 1954 [Jan. 7, 1953], No. 474/53. Class 103 (1). In a disc brake of the type in which pads of friction material are adapted to be urged into engagement with the opposite faces of a rotating disc by pistons working in opposed hydraulic cylinders, the outer ends of the cylinders being connected to a master cylinder or other source of liquid under pressure, there is combined with a friction pad or with its actuating piston a resilient stop member which comes into operation when only a small thickness of the pad remains and which holds the pad or block out of contact with the disc in the "off" position of the brake whereby a substantial increase in pedal travel is required to apply the brake. Figs. 1 and 2 illustrate one embodiment of the invention in which Fig. 1 shows a fragmentary section of one side of a " spot-type " disc brake with the friction pad 12 in new condition and backed by a hydraulically actuated piston 14 which is provided in its outer end with an axial recess and having an inwardly projecting shoulder 16 at its open rear end. A resilient stop for the piston is formed by a resilient metal U-shaped strip 17 secured by a screw 18 to the closed end wall of the cylinder 13 in which the piston operates. As the friction pad 12 wears and the piston moves forwardly until there is only a small thickness of the operative part of the pad 12 left, as shown in Fig. 2, the cranked extremities of the limbs of the stop member engage the shoulder 16. When the brake is applied the spring strip can yield to allow the friction pad to engage the disc 10, but as soon as the hydraulic pressure is relieved the spring stop retracts the piston and friction pad as shown in Fig. 2 leaving a clearance between the pad and the disc. Thus when the brake is reapplied that clearance has to be taken up and the pedal travel necessary to apply the brake is consequently increased so that the driver of the vehicle is warned that the brake requires new friction pads. In the arrangement shown in Fig. 3 a rod 20 mounted axially in a plug 21 which closes the outer end of the brake cylinder has on its inner end a head 22 working in the bore of a sleeve 23 provided in the outer end of the piston 24. The outer end of the sleeve has an inwardly directed flange 25 and a short spring washer 26 is mounted on the rod 20 between the head 22 and the flange 25. Normally, this spring washer is ineffective as shown in Fig. 3, but when the pad is neaily worn out application of the brake advances the piston to compress the spring washer and on release of the-brakes the spring washer retracts the piston and friction pad to leave a clearance between the pad and the brake disc. Other alternative arrangements to achieve the same object, such as a spring wire finger secured to the housing which is deflected by the friction pad when the pad is nearly worn out, are described and illustrated in the Specification. Specifications 688,382 and 703,213 are referred to.