Patent GB-991072-A (GB)
Title: Master cylinder
IPC: B60T11/24
Filed: 1963-12-02
Abstract: 991,072. Master cylinders; clutch control. CLARK EQUIPMENT CO. Dec. 2, 1963 [April 10, 1963], No. 47399/63. Headings F2F and F2L. A master cylinder 37, Fig. 2, for actuating control means suitable for effecting the inching and braking of a vehicle comprises a housing 39, first and second cylinders 62, 63 therein, a first fluid outlet 107 from the first cylinder, a second fluid outlet 115 frrom the second cylinder, and a fluid reservoir 92 for supplying fluid to the cylinders, and a piston assembly 64 slidably disposed in the first cylinder, a piston 75 slidably disposed in the second cylinder, a spring 82 disposed between the piston assembly 64 and the piston 75 biasing them apart so that initial movement of the piston assembly in one direction causes a similar movement of the piston 75 and forces fluid out of the fluid outlet 115 and means associated with the piston assembly 64 for forcing fluid out of the fluid outlet 107. The piston assembly 64 has two components 65, 66, one of which, 65, is fixed to it and the other of which 66, is slidable on the piston assembly 64 to a limit fixed by a snap ring 90 and the two piston components are normally held apart by a spring 70. The cylinder 63 is part of a plug member 38 and the piston 75 therein is held back by a spring 76 against a snap lock ring 79. A rod 35 extends from a crank 32 on a shaft 30, Fig. 1, which is operable by a brake pedal 20 and has an extension 85 which fits in a socket 86 in the piston assembly 64. The reservoir 92 is divided into two compartments 93, 94. The compartment 93 has a port 98 opening into the cylinder 62 and a port 100 opening into an annular space 102 behind the piston component 65 for pressure relief therefrom. The compartment 94 has a port 110 leading to a port 111 in the cylinder 63. Upon initial depression of the brake pedal 20, the rod 25 is caused to move to the right, as seen in the drawing, and shifts the first piston means 64 to the right and, through the spring 82, which is stronger than the spring 76, moves the second piston 75 to the right. This movement of the piston 75 brings an oil seal ring 80 to a position closing the inlet port 111 and effects the discharge of fluid from the cylinder 63 through a fitting 114 to a conduit 40, whereby fluid under pressure is conveyed to a piston and cylinder assembly 43, Fig. 1. A piston-rod 45 then turns crank arms 46, 49 and causes an inching valve element 16 to move to the left as seen in the drawing which effects gradual reduction in pressure in transmission clutches 14, 15, thereby permitting increasing clutch slip and reducing the drive to the wheels of the vehicle in a controlled manner. To effect braking of the vehicle the brake pedal 20 is depressed further and the slidable piston component 66 is arrested by the snap ring 90 and the space between the two piston components 65, 66 is reduced so that fluid is discharged through the port 107 and a plug 52 to a conduit 53 and thence to a pair of braking cylinders 54 associated with a pair of vehicle wheels 55. In a modification, the reservoir may omit the partition wall and the inching and braking pistons will have a common source of fluid supply.