GB1223813A - Bi-directional no-back and torque limiting unit with augmented brake feature - Google Patents

Abstract

1,223,813. Torque-limiting internal shoe drum brake. FORMSPRAG CO. 7 Feb., 1969, No. 6879/69. Heading F2E. The device comprises a brake drum, a pair of brake shows, means for transmitting rotary motion from an input member to the pair of brake shoes and means for transmitting rotary motion from the pair of brake shoes to a driven member, which means are so arranged that in operation, when excessive torque is experienced the brake shoes are prised radially outward towards the brake drum; each brake shoe has a concave seat adjacent to each end of the shoe in which is situated a hard insert whose radially outward face is a curve having a radius of curvature substantially the same as that of the brake drum, which insert can swivel in the seat, and projects above the surface of the shoe so that when the device is in operation and there is excessive torque, the hard insert contacts the brake drum to cause a braking effect. As shown in Figs. 2, 4 and 5, an input member 20 has a splined stem 21 and a flange 18 mounted in a ball-bearing 17 fixed within one end of a fixed housing 11 provided with an internal braking drum surface 16. A pair of brake shoes 26, 27, are located to the right of the radial face 28, Fig. 5, of flange 18, each shoe having a semicylindrical body portion 30 and two flange portions 32 spaced from braking surface 16 at 33. Each shoe body portion 30 has two arcuate pinreceiving seats 34, each two opposed seats accommodating a pin 36 having a rounded head 38 received in a recess 39 in input member 20. The shoes are thereby spaced at 37, Fig. 4. The shoes are normally urged towards each other by Belleville springs 47 located on a bolt and nut assembly 46, 48. The right-hand flange 32 of each shoe is provided with a radial lug 61, Fig. 5, which engages a slot in a flange on a driven member 50 splined at 62. Each brake shoe has a concave semi-cylindrical seat 67 adjacent each end in which is located a hard insert 66, preferably of silicon carbide ot chrome-treated steel; each insert 66 has a radius of curvature of its outward face which is the same as that of the brake drum, and each insert can swivel in its seat. In normal operation, the drive connection is from input member 20 through pins 36, seats 34, brake shoes 26, 27 and lugs 61 to the flange on the driven member 50. Normally the Belleville springs 47 prevent the shoes 26, 27 from being spread into contact with drum surface 16. Under a predetermined excess of input power the pins 36 are oppositely tilted reactively on their seats 34, exerting a spreading effort on the brake shoes 26, 27, which thereupon through their inserts 66 engage the drum surface 16. In Figs. 6 and 7 a fixed housing 71 has an internal braking drum surface 72 but the input member 74, is this time shown on the right of Fig. 6. Two semi-cylindrical brake shoes 77 are located between radially-extending circular flanges 78, 79 integral with the input member 74, the shoes are urged apart by compression springs 80. The flanges 78, 79 of the input member 74 are each provided with two pairs of axially aligned holes 82 receiving the ends of drive pins 83; each shoe 77 has a pair of relatively large bores 84, Fig. 6, each bore being widened at 86 to receive eccentrically, Fig. 7, an anti-friction roller 85 surrounding the respective pin 83. The driven member 75, Fig. 6, carries ball-headed pintles 88, Fig. 7, received in arcuate seats 89 on the inner chordal surfaces 90 of shoes 77. The shoes 77 have swivellable hard inserts 92 as before. In normal operation, as the shoes 77 are being driven, the anti-friction rollers 85 ride up on the eccentric ramp surfaces of the shoe openings 86, the shoes being thus urged out of frictional engagement with drum surface 72. When an excessive load torque develops, the pintles 88 separate the shoes 77 whereupon the inserts 92 make contact with drum surface 72. The pintles 88 may be replaced by a tang-type drive (Fig. 9, not shown). Preferably the interior surface of drum 16, Fig. 2, is helically grooved at 16<SP>1</SP> for coolant or lubricant; similarly, the interior surface of drum 72, Fig. 6, is helically grooved at 72<SP>1</SP>.