Patent GB-366501-A (GB)
Title: Improvements in or relating to friction clutches and brakes
IPC: F16D43/18
Filed: 1930-10-28
Abstract: 366,501. Friction brakes. PERKINS, F. A., Old Vicarage, Whitstable, and CHAPMAN, C. W., Waterford House, Rede Court, Strood, Rochester, both in Kent. Oct. 28, 1930, No. 32417. [Class 103 (i).] In friction clutches and brakes of the kind in which one or more elements pivoted to the driving member are centrifugally engaged with the driven or stationary member and are tightened by drive in the normal direction, each element comprises an arm pivoted to the driving member and a shoe pivoted to the free end of the arm, the tangent of the angle between a radius through the point of contact or centre of pressure of the shoe on the driven &c. member and a line joining that point to the pivot of the arm on the driving member being greaterthan the maximum coefficient of kinetic friction. Each centrifugal shoe 15, Fig. 1, coacting with a driven drum 12, is connected at or slightly behind its midpoint 16 by an inclined link 14 to the driving member 11, so as to be tightened or released according to the relative rotation of the parts. The shoes are retracted by tension springs 17. The tangent of the angle of inclination of the links may exceed or be less than the coefficient of static friction, in which latter case the drive is non-slipping when once engaged. Fig. 2 shows a modification in which bidirectional self-tightening is produced by oppositely-inclined struts 114 having slotted engagement 25 with their pivots 113. Alternatively, telescopic spring links may be used. Radial retracting springs 18 are provided, and their strength may be varied by bell-crank levers acted on by a control collar, which arrangement may be applied also to the unidirectional form. The shoes can be put into action at low speed by rotary cams acting on their inner surfaces, or put into and out of action by toggle or other connections to a control sleeve. The clutches may be used as brakes by anchoring the drum 12. Figs. 8 and 9 show a motor-vehicle clutch, also modifiable for use as a brake, comprising shoes 15 connected by pairs of inclined links 34 to bell-crank levers 214 pivoted at 130, the links having balance weights 36 to bring the centres of gravity of the shoes and links approximately coincident with the pins 35. The levers 214 have spring-pressed extensions 32, which can abut on the driving member 11. The weights 36 of each pair are connected by a pin 37, which is held in the position shown in a hole 38 in the lever 214 by a slight deficiency in the weight of the balance weights or by a light spring 40, or both. For smooth take-up of the drive, the tangent of angle between a radius through the pin 39 and a line joining the pins 39, 130 is greater than the maximum coefficient of kinetic friction. When, however, centrifugal force on the weights 36 is sufficient to overcome the driving thrust tending to turn the links 34 about the pin 35, the toggle 34, 214 will straighten until the parts 32, 11 contact, so limiting the load on the pins and drum, and the angle between the link 34 and radius through the pin 39 becomes less than the angle of friction. The friction flange 41 of the driven drum 12 may be pressed by a pedal 42 against the web 45 of the flywheel 28 to enable the engine to be used as a brake. A dog clutch may be used for the same purpose. The Provisional Specification comprises also a clutch resembling that shown in Fig. 1, but having an auxiliary plate or dog clutch in parallel, as in Fig. 8, the shoes having each a long toe forward of the pivot and a curved-away heel, and the arms a motionlimiting extension. The device is applicable as a brake or as a motor-vehicle sprag, the angle of thrust being then less than the angle of friction and release means being provided for use when reversing. A non-centrifugal brake is described, the stationary shoes being operated by a toggle or ramp.