GB554657A - Improvements in fluid-pressure brakes for vehicles - Google Patents

Abstract

554,657. Fluid-pressure brakes. SVENSKA AKTIEBOLAGET BROMSREGULATOR and BROWALL, B. H. Nov. 14, 1941, No. 14689. [Class 103 (i)] In vehicle compressed air brake systems, that are set for a lower or higher braking effort by a compressed air servomotor supplied through a valve operated in response to the vehicle load, the valve is provided in a conduit between the servomotor and a point in the system which is set under pressure upon a brake application but from which the pressure disappears when the brake is released if it has not already done so, and the valve is capable of shutting off the conduit only in respect of supply therethrough to the servomotor. Air losses by repeated setting movements during running are thus avoided and the changeover is effected at a substantially definite position of the valve. In Fig. 2 which shows a Hildebrand-Knorr brake, the servomotor 1 by which the "empty-load" change-over is effected is supplied from the main valve portion 10 of the system which is under pressure and at atmospheric pressure when the brake is applied and released respectively through a plug-cock 5a and is exhausted through a non- return valve 5b. The cock 5a is operated by a 3-armed lever 6 mounted on the vehicle underframe d and connected by link 7 to an axlebox. One arm of the lever 6 is in two parts, articulated for relative movement in both directions against the action of a spring 12 and another arm is connected to a dash-pot 13 whereby transmission of rocking movements of the vehicle during running are smoothed out. As applied to Westinghouse system the servomotor 1 is arranged for connection to a chamber to which the brake pipe is vented at brake applications and which is connected to atmosphere during release. The servomotor valve shown in this case is a simple non- return valve which is held open in "empty" conditions by a rod connected to a single lever mounted on the vehicle underframe and connected at its other, end to an axle-box. According to Fig. 4 a non-return valve 5 controls the connection of the change-over servomotor connected to pipe 3b with the selected part of the brake system which is connected to pipe 3a. The valve is operated by a plunger 21 and a cam-surface 20 on a dash-pot piston 18 operated against the action of a spring 17 by a lever 16, link 15 and the longer arm of a two-armed lever 14 mounted on the vehicle underframe d, the shorter arm of the lever being connected to one end of a bearing spring such as is shown in Fig. 2. The spring 17 thus takes a proportion of the load. The "empty-load" change in the braking effort may be effected by changing the leverage through which the brake cylinder operates the brake shoes as described in Specification 426,779 wherein the linkage comprises a pair of main levers connected by a pair of parallel links one of which, 27, Fig. 6, is rendered ineffective to provide the higher leverage by raising an abutment 30 pivoted in a casing 29 secured to one of the levers and through which the link extends. In the present instance, the abutment 30 is actuated by servomotor 1 controlled as above described and which may as shown be integral with the casing 29. Fig. 7 shows the application of the invention to the Kunze- Knorr freight-train brake, which, as described in Specification 106,131, [Class 103 (i)], comprises a two-chamber brake cylinder a, b and a single chamber cylinder c, controlled by a valve 'device g. Normally chambers a, b are under pressure and chamber c us open to atmosphere. The "empty-load" changeover valve comprises a plug-shaped non-rotatable body 37 containing a slide-valve 34 operable by fluid-pressure acting upon its right-hand end and upon a separate piston 35. The valve 34 is controlled by the device shown in Fig. 4, the pipes 3a, 3b being connected to the ends of the valve casing. When the brake is applied air is supplied through valves G, 34 from chamber b to chamber c as indicated. It is also supplied through passage a in the valve body 37 to the chamber b of valve 34 and to pipe 3a. If the vehicle is empty, the valve 5 is closed and as only the right-hand end of the valve 34 is thus subject to pressure the valve moves to the left. The air flowing to chamber c is thus compelled to pass through a choke c in the valve body 37. But if the vehicle is loaded, the valve 5 is open and pressure air is thus supplied to both ends of the valve 34 as indicated which is then moved to or remains in the position shown. Chamber b thus freely supplies chamber c until equalization of pressure between these chambers is effected, chamber b being thus connected to atmosphere. When the brake is released, air escapes from the chamber of piston 35 by way of chamber b valve 34, x and.g to atmosphere if it has not already escaped.