Patent GB-1420695-A (GB)
Title: Vehicle braking device
IPC: F16D65/78
Filed: 1973-05-14
Abstract: 1420695 Hydrodynamic brakes LABAVIASGE 14 May 1973 [26 May 1972] 22932/73 Heading F2E A vehicle braking device comprises an hydraulic retarder 1 which, in operation, is supplied with working liquid flowing in a closed liquid circuit including an expansion vessel 4, or a radiator 3, the retarder being filled with working liquid during a filling phase at the beginning of each period of operation and being emptied of the working fluid during an emptying phase at the end of each period of operation, a purging pipe 6 connecting a central region of the retarder to the top of the expansion vessel 4, and a valve 18 disposed in the purging pipe and having open and closed states respectively affording and interrupting communication between the expansion vessel and the central region of the retarder. There is control means acting on the valve to cause the valve to be in the open state during an initial part of the phase of filling of the retarder and to cause the valve to be in the closed state during the remainder of the filling phase, the control means causing the valve to be in the open condition during the entire phase of emptying the retarder. As shown, the closed liquid circuit comprises a pump 2, radiator 3, an engine 7 of the vehicle and a three-way, twoposition valve 8; in one position of the valve water from the engine is directed into a section 10 of the normal cooling circuit 11 of the vehicle and the retarder is connected in a loop 9 connected into the closed circuit in the other position of the valve 8. The control means for controlling the electro-valve 18 may comprise a time delay control which automatically closes the valve after a predetermined delay such control being afforded by a manostat 16, or an electrical switch mounted in the electrical supply circuit 17 of the valve 18, sensitive to the water pressure at a point P upstream of the throttle 12 which point is connected to the manostat 16 by a pipe containing a diaphragm 20 with a calibrated opening. The throttle 12 incorporates a Venturi 26 the throat of which is connected to the retarder by a pipe 25; the cross-section of the annular passage or throat formed between the wall of the Venturi and the chamber defined by the housing 28 is adjusted automatically in dependence upon the water pressure by the deformations of an elastic diaphragm 29. This latter arrangement improves the initial rise in torque since a suction effect is exerted on the gaseous volume at the centre of the retarder and accelerates filling thereof with water. To further increase the suction produced a pipe 30 may extend between the central region of the retarder and a point downstream of the diaphragm 29. Instead of connecting the central region of the retarder to the throat of the Venturi, which connection is only established when the pipe 6 is closed and through the pipe 6<SP>1</SP>, the pipe 25 is replaced by a pipe 31 connecting the Venturi to the valve 18 which then connects the pipe 6<SP>1</SP> to the pipe 31 or the pipe 6; alternatively, the upstream sections of the pipes 6 and 25 are merged. There may be means such as an electric switch 32 operable by the vehicle driver and to neutralize the automatic closing of the pipe 6.