A back-to-back proportioning valve assembly for a cross-split braking system is disclosed. The proportioning valve assembly comprises an assembly housing defining a substantially cylindrical bore extending therethrough. The bore defines first and second rear brake outlet openings. In the assembly housing are disposed a pair of inlet passages extending within the cylindrical bore connected with respective first and second master cylinder chambers. A pair of front brake outlet openings are also disposed in the assembly housing. First and second proportioning valves are positioned in back-to-back relationship within the cylindrical bore adjacent respective first and second rear brake outlet openings for proportioning the inlet pressure to the rear brake outlets. A pair of bypass channels, for bypassing each of the proportioning valves, are provided to be opened upon failure of one of the braking systems. A differential pressure piston, in the form of a cylindrical spool, is disposed within the cylindrical bore to overlie the bypass channel ports. Upon failure of one of the braking systems, the differential piston shifts, thus opening one of the bypass ports and providing a direct fluid communication path from the inlet passage to the rear brake outlet opening, thus bypassing the proportioning valve.
An object of the present invention is to decrease the machining cost and to improve the productivity. A liquid pressure control device (21) for load responding brake comprises a valve mechanism (25), which is slidably disposed in a housing (22), for decreasing the liquid pressure of a master cylinder in a predetermined proportion and transmitting the liquid pressure to a rear wheel brake cylinder by the movement of a plunger (24) operated in response to the liquid pressure from the master cylinder; and a load sensing mechanism (27) in which a load depending on the movable load of a vehicle is applied to the plunger (24) so as to move the pressure decrease operation start point of the valve mechanism (25). The housing (22) is formed by cutting a long material (50) formed by extrusion or drawing to a predetermined length and then by machining the cut material (51).
A dual proportioning valve assembly (10) for a vehicle braking system comprises a housing (12) having a pair of inlets (29, 30) and outlets (31, 32), a bore (25) within the housing (12) containing a pair of oppositely disposed differential pistons (40, 140) biased apart by a main spring (200). The first and second differential pistons (40, 140) have associated first and second poppet valves (50, 150) which control fluid flow between the respective inlet and outlet. A cage member (60) extends within the first differential piston (40) and is connected with the first poppet valve (50), the cage member (60) extending longitudinally within the bore (25) and having an interior chamber (70) with an inertia-sensing mass (80) therein. The inertia-sensing mass (80) engages a third poppet valve (94) which controls fluid flow between the interior chamber (70) and a variable volume chamber (100) defined by the cage member (60) and a stationary piston ( 160) which engages the cage member (60). The stationary piston (160) abuts a shoulder (13) of the housing (12) and extends into the second differential piston (140) where it is connected with the second poppet valve (150) controlling fluid flow between the respective inlet (30) and outlet (32). The stationary piston (160) and cage member (60) are biased apart by a plunger spring (205).
A free piston is reciprocally disposed within a first plunger unit associated with one of two circuits which plunger also houses a poppet valve actuatable by the free piston. A second plunger is reciprocally received in one end of the first plunger unit and also has a poppet valve actuatable by the free piston. The second plunger is biased toward the first by an actuator piston/spring arrangement subject to control by a valve responsive to vehicular deceleration. During pressure modulation the free piston reciprocates back and forth rapidly, opening and closing each of the poppet valves. Upon failure of one of the dual circuits both of the plungers shift in the same direction causing one poppet valve to remain open and prevent pressure modulation. Upon failure of the other circuit, the pressure transmitted by the arrangement markedly increases to produce the necessary deceleration to close a deceleration sensitive valve and induce modulation. Further, the lack of bias on one end of the free piston elevates the modulation point at which the other poppet valve begins modulation whereby an adequately high pressure is discharged.
An isolation valve device for a hydraulic brake system of a railway vehicle including passageways via which hydraulic pressure communication is established between a pressure controller and the brake units of each truck of a railway vehicle, and a bore to receive a pair of piston valves adapted to interrupt hydraulic pressure communication in a respective one of the passageways leading to the different truck brake units, when a pressure differential occurs therebetween, due to a ruptured brake line at one of the trucks, for example, causing a hydraulic fluid leak thereat.
A safety system for hydraulic brakes in a train brake system wherein a spring biased spool valve controls delivery from a hydraulic fluid source to at least two sets of spring applied hydraulic brake actuators and wherein said spool valve is also biased by the fluid pressure delivered to said two sets of brake actuators and upon a rupture in a brake line delivering fluid to one brake actuator, which causes a lowering of a fluid pressure force on the spool valve, causes the spool valve to shut off the delivery of fluid to the ruptured line to allow the spring applied hydraulic brake actuator to engage the applied brake.
