GB1443968A - Trailer vehicle brake control valve units - Google Patents

Abstract

1443968 Trailer brake relay valve assembly ROBERT BOSCH GmbH 19 Oct 1973 [20 Oct 1972] 48807/73 Heading F2F A trailer vehicle brake control valve unit is operable to control the pressure in a trailer brake line 26 in dependence upon the brake pressure in at least one of two tractor brake lines 5, 10 or in dependence upon the pressure in a spring-loaded brake-operating mechanism circuit. The valve unit comprises two brake pistons 2, 3, a brake pressure chamber 6 above the piston 2 being connected to brake line 5 and a brake pressure chamber 11 located between the pistons 2, 3 being connected to brake line 10. An atmospheric air chamber 15 is located on the other side of piston 3 and within chamber 15 is arranged a stressed spring element comprising springs 17 acting on the outer piston part 20 of a two-part retroactive piston 20, 21. Inner piston part 21 which is acted upon by a spring 22 is mechanically connected to piston 3 by axial extensions 19. The piston 20, 21 forms the movable wall of a pressure charge chamber 27 connected to the trailer brake line 26 and a fixed wall 28 of the chamber 27 carries an inlet valve seat 29 of a double-seat valve 29, 30, 31 whose outlet valve seat 30 is formed on the piston part 21. The valve closure member 31 of the double seat valve 29, 30, 31 has a sealing lip 31<SP>1</SP> by means of which the closure member 31 slides on a tubular member 32. The tubular member 32 has at least one radial opening 37 for connecting the chamber 27 to atmosphere; the tubular member 32 has a flange 33 by means of which it can act upon the piston part 21, and the tubular member 32 carries a piston member 34 one side of which is subjected to the supply pressure of air supplied to a chamber 35 and the other side of which is subjected to the pressure of air in a chamber 36 connected to the spring-loaded brake operating mechanism circuit. In use, pressurization of one or both brake lines 5, 10 causes piston 3 to move (with or without piston 2) and via axial extensions 19 the piston part 21 is moved to close outlet valve 30, 31 to cut off communication between the atmospheric air and the trailer brake line 26, and thereafter open inlet valve 29, 31 to connect chamber 27 to chamber 35 to cause compressed air to flow to trailer brake line 26. The pressure in the trailer brake increases steeply relative to the increase in pressure in the tractor brake until the brake piston 3 abuts an annular shoulder 23 on the outer piston part 20 whereafter the piston 20, 21 acts as though it were one piece and the lead of the trailer brake pressure is terminated. In response to a drop in pressure in the spring- brake operating mechanism as caused by a defect or deliberately by a parking brake valve or auxiliary brake valve the piston 34 and tubular member 32 move downwardly; the flange 33 pulls piston part 21 downwardly to change over the double seat valve 29, 30, 31. The reactive effect upon the piston member 34 is effected solely by the inner piston part 21: this reduces the lead of the trailer brake pressure.