Patent GB-1217028-A (GB)
Title: Relay valve unit for trailer brake systems or the like
Inventor: MANN TORSTEN LARS TEODOR
IPC: B60T15/20
Filed: 1968-10-11
Abstract: 1,217,028. Compressed-fluid braking systems; tractor-trailer systems. T. L. T. MANN. 11 Oct., 1968 [13 Oct., 1967], No. 48407/68. Heading F2F. A relay valve unit for a trailer brake system -which system includes a conduit to a reservoir (e.g. compressed air) on the trailer, a supply conduit to the trailer brake cylinders, a feed conduit connectable to a pressure source on the tractive vehicle, and an actuating conduit for variable pressure supply to the valve for intentional brake operation-comprises a valve housing with connections for all the conduits, a reciprocatory relay piston rigidly connected to a tubular part formed as a valve slide cooperating with the valve housing, and a reciprocatory brake release piston formed as a further valve slide in, and co-operating with, the tubular part, and co-operating with the valve housing, the brake release piston providing automatically for supply of pressure fluid from the reservoir to the brake cylinders via the corresponding conduits and the valve housing in the case of a pressure void in the feed conduit. As shown, a brake release piston 4 is slidable in the tubular part 3 integral with a relay piston 2 slidable in a valve housing 1. D is for connection to an actuating pressure conduit, C is for connection to the trailer brake cylinders, M is for connection to a pressure source on the tractive vehicle, and R is for connection to a pressure reservoir on the trailer. In all situations when the trailer is not separated from the tractive vehicle, pistons 4 and 2 are in the relative positions shown in Fig. 2, where pressure at M forces piston 4 against top 7, spring 5 being thereby compressed. In the brakes off position (Fig. 1, not shown), the beads on top 7 are in contact with the top of housing 1, pressure at D being absent, and brake cylinder connection C is at atmospheric pressure through aperture A which is not then obturated. M supplies R through holes 9 and 10. For partial application of the brakes, Fig. 2, pressure fluid admitted at D forces piston 2 downwards, and as soon as the lower end 6 of brake release piston 4 has begun to obturate aperture A, flange 15 has cleared sealing portion 16 to connect R with C. In the full braking position (Fig. 3, not shown), pistons 2 and 4 are in their lowermost positions, and M and R are still connected through holes 9 and 10. On separation of the trailer from the tractive vehicle, intentionally for parking or on trailer breakaway, pressure at M from the tractive vehicle pressure source is lost, whereupon the raised position of piston 4 can no longer be maintained because spring 5 can now expand. In this situation, Fig. 4, piston 4 has obturated aperture A, and has opened communication past sealing portion 16 between the reservoir connection R and brake cylinder connection C; at the same time, extension 17 of piston 4 has co-operated with part of tubular part 3 to cut off communication between M and R to prevent loss of pressure from the reservoir on the trailer. This is the parking or emergency braking position. It will be observed that piston 2 is in its uppermost position because no pressure has been applied at D. In the modification of Fig. 9, the valve housing 1<SP>11</SP> and relay piston, &c., 2<SP>11</SP>, 3<SP>11</SP> are almost as before, except that in the housing a non-return valve 40 is provided between connections M and R. The spring between the brake release piston 4<SP>11</SP> and top 711 is omitted, and the piston 411 is shaped differently; also, a further passage 43 is provided in piston 4<SP>11</SP> to establish communication between the annular upper side of this piston and the region around neck 18<SP>11</SP>; in addition, the upper portion 41 of piston 4<SP>11</SP> makes sliding contact with the upper portion of tubular part 3<SP>11</SP>. This modification works in the same way as the embodiment previously described. Fig. 9 shows the full braking position. Figs. 5 and 6 (not shown) depict a practical embodiment of the device which, functionally, differs slightly from those above described. The fluid supplied at connection D need not be of the same kind as that supplied at connection M.