GB1415624A - Load dependent brake operating device - Google Patents

Abstract

1415624 Load-dependent braking; valves KNORR-BREMSE GmbH 23 Jan 1974 [23 Jan 1973] 03237/74 Heading F2F A load dependent, fluid pressure operated brake system comprises a spring applied brake cylinder 1, a load responsive valve 2 connected to the cylinder 1 to control the pressure therein for brake application and release, a brake control valve 3 connected to the valve 2 to control operation thereof, and a pressure reducing valve 4 arranged in a fluid pressure line upstream of both valves 2, 3 which valve 4 is adjustable to control the maximum pressure available to valves 2, 3 and hence to cylinder I to release the brake. The embodiments illustrated utilize compressed air as the fluid pressure though it is envisaged that the fluid pressure could be an hydraulic liquid. In the embodiment of Fig. 1 a common compressed air line 9 for valve 2 and valve 3 is connected by means of valve 4 to a main storage vessel pipe line 10. The valve 2 comprises two regulating pistons 11, 12 defining respectively chambers 15, 16 and 17, 18 and operable by means of rams 19, 20 on a scale beam 21. The beam 21 has a movable pivot constituted by a roller 22 connected by a crank drive 24 to a piston 26 which is acted on by a load dependent pressure fed to an inlet 7 by a relay valve (not shown). A further ram 29 on the beam 21 has a valve plate 30 co-operable with a seat 32 to form a discharge valve to atmosphere. The seat 32 is formed on a sleeve 31 whose base part 44 cooperates with a seating 43 on an axially bored part 42 to form an entry valve for a chamber 36. The chamber 36, which connects with the inside chamber 35 of the sleeve 31 via penetrations 34, is connected to the cylinder 1 via a line 48, and a chamber 45 is connected to line 9 via a line 46. The chambers 16, 18 are also connected via a line 47 to line 9, the chamber 15 is connected via a line 50 to valve 3, which in this embodiment is an electrically operated valve, and the chamber 17 is connected to line 48 via a line 49. With the line 10 ventilated, as for example when the vehicle is halted, the chambers 16, 18, 45 are pressureless and the brake control valve 3 cannot feed compressed air into chamber 15. Inlet valve 43, 44 is held open by the action of a spring 39 and chamber 45 is connected to chamber 36 whereby the chamber 17 is not pressurized. The cylinder 1 is thereby caused to give full spring actuation. When the line 10 is filled with compressed air and with valve 3 in its released position a pressure reduced by valve 4 builds up in chambers 15, 16, 18 and in chamber 45 and via open valve 43, 44 in cylinder 1 to give brake release. For brake application the valve 3 is operated to reduce the pressure in chamber 15 which causes beam 21 to pivot clockwise about pivot 22; the position of pivot 22 defines lever arms a, b-for a fully loaded vehicle a and b are equal and as the load is reduced a decreases. As the beam 21 pivots clockwise ram 29 is moved to open valve 30, 32 to connect the cylinder 1 to atmosphere to cause braking, the pressure in chamber 17 decreases until equalization of forces acting on the beam 21 occurs, the forces varying in accordance with the lengths of the lever arms a, b and the pressures in the chambers. As the load decreases, the greater is the residue pressure in the cylinder 1 and the less the braking forces. The brake control valve 3 may take the form of a seven stage brake control valve to give a stage-wise pressure reduction or the pressure reduction may have a linear characteristic. In the embodiment of Fig. 2 (not shown) the chamber 16 as well as chamber 17 is connected to the cylinder 1. In this embodiment the roller 22 takes up a position at the extreme right of beam 21 when the vehicle is fully loaded, and moves to the left as the load decreases. In the embodiment of Fig. 3, the valve 3 is replaced by a purely pneumatic brake control valve 53. The valve 53 is connected to a line 54 having a falling control pressure characteristic controlled by a guide brake valve. The line 54 serves as a source of compressed air for line 9-a relief valve 56 opening towards the reducing valve 4 is connected between line 54 and valve 4 and a tank 57 is filled via valve 56.