Patent GB-484108-A (GB)
Title: Improvements in or relating to spring controlled mechanism
IPC: B60T8/20
Filed: 1936-10-31
Abstract: 484,108. Spring mechanisms. CARWARDINE, G. Oct. 31, 1936, No. 29651. [Class 108 (iii)] [Also in Groups XXXIV and XXIV] A brake-operating mechanism which may also be used for operating clutches comprises a brake-applying spring which remains inoperative while the pedal is moved until the engagement of the shoes with the brake drum causes reaction in the transmission which renders the spring operative by means of a clutch. The spring is moved past dead centre when it is required to exert brake applying force. The clutch may couple the spring to the transmitting mechanism or merely couple the mechanism to a fixed part to form an abutment for the spring to act against. In the modification shown in Fig. 1 the pedal 1 applies the brakes through a spring 4, lever 2 and a rod 5. When the spring 4 yields due to tension in the mechanism, teeth 8 on a lever 7 are drawn by hub 11 into engagement with teeth 10 on a pivoted member 9 connected to the brake-applying spring 15 which is thereupon moved past its dead-centre position and assists brake application. The energy stored in the transmission is sufficient to overcome the spring 15 and release the brakes. In a further modification the brakes are first applied by levers and links held in the initial position by a spring, yielding of which produces the turning of a lever and the gripping of a square shaft by means of clutch shoes. The square shaft is the actuated shaft of a spring servo unit as shown in Specification 461,970. The shaft has a spring connection with the servo unit to allow brake application if the unit should fail. In a modification of this latter construction a clutch having wedge members is adapted to engage between the shaft and an external member surrounding the shaft and connected to the brakes. In a further modification a. clutch shoe is drawn against the shaft by bell-crank levers carried by rollers engaging the other side of the shaft. In a further modification disc like members on a single shaft are adapted to move together until a spring connection yields whereupon balls in recesses cause lateral relative movement of the discs and the gripping of a further disc which moves struts past a dead-centre position to allow the brake applying spring to exert its pressure on the system. In the modification shown in Fig. 6 the brake pedal 62 operates the brakes connected to a lever 68, through a spring 69. A link 64a also connects levers 62, 68, has a pin- and-slot connection with the lever 68. Toggle links 70 are held by the servo spring 73 between the link 64a and links 71, the centre of the toggle abutting against a link 72. These members with bell-cranks 74, 75, pivoted on a U-shaped clutch element 78 move as a unit when the brake is applied until the brake shoes engage the drums, whereupon the lever 68 is held stationary, and the clutch element 78 and bell-crank levers 74, 75 are stopped by the lever 68. The link 64a carries the toggles 70 past the dead centre position and the bell-crank levers 74, 75 are moved and by means of links 84, 85 cause a shoe 82 to move so that a fixed rod 83 is gripped between the shoe 82 and the clutch element 78, thus forming an abutment so that the servo spring 73 exerts pressure on the brakes through the toggle 70, link 64a and lever 68. A further modification comprises a rearrangement of this construction in which a lever on the pedal shaft forms a part of a toggle which moves past its dead centre when the brakes engage and by means of levers and links causes the engagement of the fixed abutment clutch and brings the servo spring into action. In a further modification in which a pedal lever forms part of a toggle of which the servo spring forms the other part, these parts move as a unit and carry a roller which runs on an arcuate fixed rail until the brakes engage whereupon the toggle passes its dead centre and the fixed rail is gripped between the roller and a clutch sheet and the servo spring exerts its force on the brakes. In a further modification the clutch shoe and roller are adapted to grip two arcuate rails held separate by rubber blocks and adapted to grip between them, when the clutch engages, a pad of friction material adapted to be carried round with the mechanism by pins on the mechanism. Inertia weights may be used to prevent premature engagement of the clutch. Specification 377,251 also is referred to.