Shunts and Shunting

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hat good would all those beams do, if we could not shunt vehicles from one beam to another? Shunts will be needed: at nodes; places where beams meet and separate for sidings at stops; so that stopping cars wonīt be in the way of those passing thru when branching out, where parallel beams are required in order to increase traffic capacity at crossings and roundabouts at station areas and terminals for servicing the beams (see further down)	This is a rather technical page. But we will only deal with 4 subjects: The shunts The "Frog" problem Where to place the shunts Service and maintenance of the beams

1. The Shunts

Figure 1.

rom a functional point of view, we have to divide the shunts into 2 categories, depending on how the cars have to negotiate them: Those shunts where the beamcars donīt have to reduce speed Those shunts where some reduction of speed is required. Actually, it is not as simple as stated above. Reduce from what speed? Every single shunt will, because of its design, have a maximum allowed speed. If a certain shunt is placed on joining (or diverging) beams that do not allow high speeds (whatever our definition of "high speeds" happens to be), then the beamcar can pass thru that shunt without reducing speed. If the same shunt is placed on beams that do allow high speeds, then, of course, that shunt would belong in the other category, the one that requires beamcars to slow down. A well-designed shunt will not by itself cause any jerk to the beamcar, because of any sudden change of direction. The shunting should be quite smooth. But one or both of the joining beams might have sharp curvatures in connection with the shunt.

This is governed by the logistical necessities of the area where the shunt is situated; there might not be enough space to allow for a smooth shunt. Looking at illustration in figure 1 above, it is obvious that in the shunt A, the angle a is small enough to allow the beamcars to pass through while maintaining a "rather" high speed. This shunt then belongs to the first category. Looking at shunt C, it is equally obvious that the cars would need to slow down, so that the passage does not become too jerky. This is not just a matter of comfort; it causes wear to both beam and beamcar to subject the beamcar to too strong sideways strain. The middle shunt (B) belongs to the second category, as well as the shunt C. Although the angle b might not be bigger than the angle a, the change of direction for those cars turning right would be just as sudden as those going through shunt C.

So, what is the critical angle or bending radius in this context? Well, that would depend on the speed allowed on the beam in question; the lower the speed, the larger the critical angle (and the smaller the bending radius) could be. It is also a question of how much jerk one is prepared to accept. This, in turn, would depend on whether the beamcar is empty, carrying passengers or carrying freight. If you have studied the concept of timeslots on these webpages, you will appreciate why this categorizing of shunts is rather important. Whenever possible, one should opt for shunts where slowing down is not required, because it makes for easier control of the traffic if the beamcars can maintain a certain speed. The cars could keep their places in their assigned timeslots, and extra signalling and sensors to regulate their speeds could be dispensed with.

2. The "Frog" Problem

he shunting can be done in different ways. The "normal" old-fashioned method is to let the shunts do the shunting. SwedeTrack System quickly realized that such a method was not good enough to enable the beamcars to pass shunts on close succession (i.e. less than a second between cars). SwedeTrack needed something much better. And that method is described on a separate page. Figure 2:4 at right (a cut-through view from above) shows how the inner part of the runway, where the beam splits in two (yellow), cannot be supported in any way, other than by adjoining parts of the runway, which are supported by the crossbeams marked "S". This is because, even though we might put a support over the shunt, it could not carry the bottom flange (yellow) because any vertical structure in the yellow area would be in the way of the propulsion vehicle. This is called a "frog" in railway terminology. Even if these crossbeams are placed directly above, they cannot "reach" this part of the runway. For an abrupt shunt like in figure 2:4 this might not be a problem. But, as can be seen in figure 2:5 (which likewise shows a cut-through view from above), there can be quite a distance between touch-down points in a smooth shunt, and the area indicated with yellow cannot be supported in any way, neither from above nor from below; half of the supporting structure has to be removed. The left branch would be supported on the left side and the right branch on the right side. The middle part (right side of left branch, left side of right branch) couldn't be supported again until the complete beam was reformed on each branch unless it was somehow supported from below via a very long span. Figure 2:3 The cut-hrough view of a shunt in figure 2:3 above illustrates the dilemma. The runways (B in the figure) are normally supported by the sides, but these sides have to be removed at shunts. Vehicle designs could compensate for this up to a point, as has been done in the FlyWay® concept, but this is nevertheless a fairly serious design issue. The smoother the shunt, the longer would this span be. For example, at a speed through the shunt of 40 m/s (i.e. 144 km/hour), one would probably have to consider a span of at least 30 meters having an unsupported central part. There has to be design compromises here, involving: Using strong and thick beam materials at shunts. Using not-so-smooth shunts (to shorten the length of the frog). Using very deep lateral supports from the nearest vertical support, which would require the vehicles to hang well below the guideway (indicated by"D"in figure 2:6). Shift the vehicle loads away from this unsupported runway as much as possible. This could be done by some mechanism where the vehicles going through the shunt shift much of their weight to the supported, outer runway (indicated in figure 2:5). Accept a maximum speed through the shunts that are low enough to enable rather abrupt angles at the shunt. This would make these unsupported tongues shorter. Detailed beam illustrations can also be found on web-page 36.

Figure 2:4. Figure 2:5. Figure 2:6. Comments to figure 2:6: By using thicker beam material underneath the inner runway in a frog, it can be made to withstand heavier loads. But this also means that the cabins might have to be lowered (whether they are equipped with lifts or not) in order to clear this reinforcement ((indicated by"D"in the figure).

3. Where to Place the Shunts

Figure 3:1.	Figure 3:2.

enerally speaking, shunts will reduce speeds on the beams. For the price of more beams, one would not only increase total traffic capacity but, more important in this context, reduce the impact of shunting on traffic performance. Figure 3:1 gives a simple example of this. By joining several consecutive stops with extra beams, as shown to the right in the figure, the control system has the choice of better optimizing traffic flow. If car 3 is destined for stop B and car 2 is destined for A, the alternative at left would require car 1, which is going straight thru without stopping, to slow down both at shunts A and B, because it will have vehicles 2 and 3 immediately ahead of it.

But if both cars (2 & 3) were to shunt off at A, car 1 would only have to slow down at shunt A. Likewise, when cars 2 and 3 leave their berths, they could both do so at shunt C. Admittedly, it would take some calculations as to the nature of the traffic in each situation, to judge whether it is worth the trouble to make this kind of arrangements. Consideration would of course have to be taken to: how smooth the shunt is how heavy the vehicles will be. Small vehicles accellerate quicker.

Another example is shown in figure 3:2. The vehicle destined for D would, in the first alternative, have to slow down at each of the shunts A, B and C. In the other alternative, the 3 shunts have been gathered close together in the yellow area. The vehicle would have to slow down only once, and then be able to pick up speed again. Thus, for the price of more beams, shunts could be placed in such a manner that vehicles are less hampered by them, and the average speed of vehicles could be kept higher.

4. Service and Maintenance of the Beams

t must be possible for service personnel to get inside the beams for maintenace work and for inspection. Possible solutions are, of course, to provide hatches on one side, or on the top, at regular intervals on the beams. Not ideal solutions, for 3 reasons: This would make beam segments slightly more expensive to manufacture More types of beams would have to be kept in stock; those with hatches and those without (unless one put hatches on all manufactured beam segments) For hatches on the side, it would be difficult to avoid power cords and cables; they would have to be moved to the other side of the beam, which reduces flexibility. For hatches on the top; how would the wave guide be handled? A removable section under the hatch? Not impossible to solve these problems, of course, but there is a better solution: Extra shunts that terminate in hatches instead of shunts, as shown in the illustration to the right, where the beams are seen from above. This way, it would also be easier for both service personnel and small service vehicles to enter and leave the beams.