Patent GB-727698-A (GB)
Title: Improvements in hydraulic-pressure braking systems
IPC: F16D65/22
Filed: 1953-01-20
Abstract: 727,698. Hydraulic brakes. DUBOIS, M. O., and DUBOIS, B. M. Jan. 20, 1953 [Oct. 1, 1952], No. 1610/53. Class 103 (1). A wheel cylinder or receiving device for a hydraulic brake system comprises, between the source of liquid pressure and the receiving cylinder of the brake, an auxiliary cylinder disposed in the same block, in which moves a piston provided with a valve adapted to ensure a constant return travel of the braking friction element or elements, the piston and valve provided therein being arranged in the form of a mobile unit of very small size. The brake system illustrated in Fig. 1 is of the known type comprising a pedal operated master cylinder 5 applied with liquid from reservoir 5a. Under the action of the pedal operated piston 4 liquid is discharged from master cylinder 5 through pipe lines 6<SP>a</SP>, 6<SP>b</SP>, 6<SP>c</SP>, 6<SP>d</SP> leading to the wheels of the vehicle. One such connection is shown for the pipe line 6<SP>c</SP> to a connection 7 in the receiving device (Fig. 2). This device comprises a block 8 rigidly secured to the wheel brake back plate 9. The principal cylinder 11 and the auxiliary cylinder 10 are disposed in this block at right angles to each other as indicated in Fig. 3, which is a section at 3, 3 of Fig. 2. Liquid is received via connection 7 and passages 16 and 15 into the auxiliary cylinder 10 thus forcing the piston 36 to the operative position shown in Fig. 3. The piston 36 is reduced in diameter at 37 and carries a single sealing cup washer 38 of elastic material. The piston 36 is provided with a hole within which is housed a spring applied valve 46 which is seated, in the inoperative position, on the seating 44. An axial portion 51 of the valve 46 carries an axial push-rod 52 which is both longer and smaller in diameter than the passage 43 of the piston 36. Thus when the piston is forced under liquid pressure to the operative position abutting the plug 14 as shown in Fig. 3, the valve 46 is raised off its seat and liquid passes via holes 49, passage 43 and notches 36a into the chamber 29 of the principal cylinder 11 thus forcing apart the pistons 22 to operate the brake shoes through connecting rods 24 which are sealed against the ingress of dust &c. At the end of the operation, the brake pedal is released and the return spring 27<SP>a</SP>, 27<SP>b</SP> of the shoes 25 causes the pistons 22 to return to their inactive position and thus returns the piston 36 to its original inoperative position. The strength of the spring 47 of the valve 46 is such as to allow the pressure on the principal cylinder side of the piston 36 to return to a value just greater than the residual pressure that the return spring 27<SP>a</SP>, 27<SP>b</SP> exerts on the shoes 25. Hence the piston and valve device in the auxiliary cylinder 10 ensures a constant return travel of the brake shoes. If during prolonged braking a rise in temperature results in distortion of the brake drum, the pressure exerted on the brake shoes is controlled by the strength of the return spring 47 of the valve 46 which allows the valve to rise off its seating thus bringing about a reduction of pressure. Brake adjustment may be varied by screwing or unscrewing the plug 12 which may be locked in the adjusted position, so that the stroke of the piston 36 may be varied. A modification of the invention is described and illustrated in which a pivotally mounted single shoe is operated by a single piston movable in a cylinder and an auxiliary piston, having a valve 46 as described above, is movable within a cylindrical body disposed axially in the cylinder.