Self-energising electro-hydraulic brake (SEHB) ant that is going to be further pursued in future. 6 Concluding summary and prospects The whole of the concept presented above was arrived at through careful consideration of both functions and costs. It has been decided that for the further development of the research project supported by the German Science Foundation the principle to be used is to be that of external radial guidance by a four-piece lever drive in combination with an open hydraulic circuit. The force necessary for a parking brake is to be provided in two stages. Firstly, a spring on the brake actuator is to provide a minimum parking-brake force for an unlimited period of time, even in the absence of a connection to an external energy supply. Secondly, the installed pump is to support the parking-brake force temporarily as required. In addition to that, the intermediate-pressure reservoir can be continuously pressurised by the pump, ensuring that a constant braking force is always available. The inclusion of a pump naturally increases the costs. Since, however, only a constant pump for a low pressure level is required, a very low-cost pump is perfectly adequate for this purpose. A detailed design of the functional prototype of the improved self-energising electrohydraulic brake is now to be drawn up on the basis of the solution discussed here. The dynamics of the build-up of the braking force increase with increasing self-energisation. In order to counteract this effect, it is still necessary to have a 2/2-way valve with proportional characteristics free from leaks in its closed state. The volume flow through the valve could thus be adjusted to the brake’s working point. Valves of this nature are currently not available on the market, but they would be of interest in many applications with energy-efficient hydraulic systems. The IFAS itself is working on the development of valve prototypes with the properties mentioned. These are being tested on the rig referred to above in combination with the implementation of non-linear control algorithms. Once all this has been completed, the build-up of the braking force ought to behave stably over the whole working range in combination with simplified valve control and additional convenience. port force acts on the piston rod. One of the pistons is moved along as well in the direction of the force, whereas the second piston is blocked by its end stop. Each of the pistons can only move as far as the middle stop. This makes it possible to position the drilled hole for the oil connection in a permanent location in the middle of the support cylinder. If the height of the piston’s ring gap is sufficient, the oil connection can be made, as an alternative, through a hole drilled in the movable piston. This makes it possible to use a shorter cylinder without reducing its stroke, because the middle stop becomes superfluous and it becomes possible to move the pistons until they are alongside one another. Essential advantages of the “rod plunger” are the direct application of the force and the simple fastening to the brake and bogie. All the components can be manufactured for little outlay. For this reason, it is this variTwo possible versions of a support cylinder with just one hydraulic chamber are presented in Fig. 4. The first of these is based on a special version of a plunger cylinder, and the second is derived from a synchronous cylinder. The “housing-plunger” variant has two plunger rods arranged in a moveable chamber. This chamber is surrounded by a fixed housing with a guiding groove machined into it. The supporting force is transferred to the moveable chamber via two lugs. The force is supported, in turn, through the oil and the piston on the housing. The other piston is made to move as well by engaging an end stop. What characterises the “rod-plunger” concept is that there are two moveable cylindrical pistons inside one housing. A piston rod is fed through both pistons and they are able to move along it. The cylinder barrel is fastened to the bogie, whereas the supFig. 4: Concepts for double-acting plunger cylinders Oil connection Pistons Pressure chamber Oil connection Pistons Fixed housing Housing plunger Rod plunger Railway Signalling & Interlocking International Compendium &EJUPST (SFHPS 5IFFH t 4FSHFZ 7MBTFOLP Technical Data: 3BJMXBZ 4JHOBMMJOH *OUFSMPDLJOH *4#/ BQQSPY QBHFT 4J[F DN Y DN )BSEDPWFS Price: û QPTUBHF For more information please visit www.eurailpress.de/irsien
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