GB742876A - A self-adjusting wheel cylinder for hydraulic brakes - Google Patents

Abstract

742,876. Hydraulic brakes. BELENKIJ, J. Jan. 7, 1953 [Jan. 15, 1952], No. 501/53. Class 103 (1). A self-adjusting wheel cylinder for vehicle braking systems comprises main pistons acting upon the brake shoes or similar members, auxiliary pistons, and further components adapted to form a closed space or spaces of variable volume between the main pistons and auxiliary pistons such that the space or spaces referred to are provided with overflow means which enables the liquid both to be admitted into said spaces and to be discharged therefrom when the pressure inside these spaces rises above a predetermined limit. The selfadjusting wheel cylinder 1 comprises two main pistons 2 acting upon the brake shoes, through thrust members or the like, and auxiliary pistons 3 which are free to move within the space confined by a central stop member 5 and by fixed partition members 4. Between both auxiliary pistons is a space 15 which is in communication with the main brake cylinder. Spaces 16 are formed between each auxiliary piston 3 and the opposite main piston 2 via apertures 19 in the fixed partition members 4 and each auxiliary piston 3 is provided with a spring-loaded overflow device 9, 10, 11 which allows, under conditions specified below, the passage of liquid from space 15 to spaces 16 and vice-versa. In the basic position shown, the auxiliary pistons 3 are urged against the central stop member 5 by means of springs 12. Vent screws 14 are provided through which air may be expelled from the spaces 15 and 16 prior to the initial operation of the unit. When the vehicle or aircraft brake is operated, the auxiliary pistons 3 move, under the influence of hydraulic pressure in space 15, towards and bear against each partition member 4. Projections 17 on the partition members 4 strike the valve balls 9, as shown in Fig. 2, and enable liquid to pass from space 15 into spaces 16 so that the main pistons are able to produce the necessary stroke to apply the brake shoes. Movement of the main pistons 2 is stopped when the pressures inside the spaces 15 and 16 are balanced so that the auxiliary pistons are pushed back by the action of springs 12 and the valve balls 9 move back on their respective seats. When it is intended to release the brake, the pressure inside space 15 is reduced and the main pistons 2 commence their return movement and the liquid within the spaces 16 pushes back the auxiliary pistons 3 against the central stop member 5. The lower limit of the force of each spring 11 is such that when the normallyoccurring excess pressure inside the spaces 16, due to the action of springs which pull the shoes towards each other, takes place it is not sufficient to open the ball valves of the auxiliary pistons. The upper limit is determined by the fact that any excessive pressure inside spaces 16 occurring in an unbraked condition due, for instance, to pressure of the deformed drum, due to heat, acting on the brake shoes, the liquid must be free to pass from spaces 16 via a calibrated aperture 18 in each overflow device, to space 15, thus allowing the main pistons 2 to return to their inoperative positions. Specification 742,395 is referred to.