Why this elaborate train consist? I would like to take a closer look at the technology:
Up to and including the Re 6/6, the SBB and all other railways procured step-switch locomotives. These increased the traction power in stages by means of taps on the transformer. This sudden increase in tractive power (clearly noticeable in the carriages behind the locomotive) only allowed very simple skid protection. The options available when skidding occurred were sand, the brake block and switching back one or more stages.
This changed dramatically with the appearance of locomotives with gating control (with choppers on DC railways), and later with inverters. Now the tractive force could be changed quickly and steplessly, which made it possible to push the start of the skidding to its limits.
During extensive adhesion test runs with the BLS Re 4/4 161 and the RhB’s Ge 4/4 II, it was discovered that a macroslip of 3 to 5 km/h was the best way to get the most torque onto the rails, i.e. the highest tractive force. Macroslip means that the locomotive’s wheel turns a few kilometres per hour faster than the locomotive itself is moving translational. The leading wheel usually turns the fastest, as it encounters the worst rail conditions (the macroslip leads to a “cleaning” of the rail surface thanks to the heat and friction energy released). In addition, as experts know, there is of course the load release of the leading wheel due to the lever arm effect of the acceleration forces in the bogie.
The HGe 4/4 II was therefore one of the first locomotives to benefit from this knowledge during the design phase. The aim was to try to achieve a state with controlled macroslip, which seemed feasible thanks to fast analogue controls. From today’s perspective, these were of course only initial attempts, as analogue electronics could only be used to implement limiters, adders and multipliers and optimisation could only be achieved with difficulty by soldering and unsoldering resistors and capacitors with different nominal values. Fast computers that allowed online software changes and simulation software were unthinkable at the time.
To create a dirty rail, a solution of soft soap was sprayed onto the track in front of the HGe 4/4 II. The car train together with the electrically braked Ge 4/4 III served as a trailer load. In the tunnel, the train was stopped on gradients and then accelerated again and the behavior of the locomotive wheels was recorded. Conclusions were drawn from the recordings as to the direction of optimisation for the next journey.
After a few journeys, the following could be experienced as an observer in the driver’s cab: the train is at the passing station in the centre of the tunnel. After the crossing train has entered, the stopcock for spraying the soft soap is opened and the driver is instructed to “turn the handwheel to the stop and then leave it there”, i.e. pre-select the maximum acceleration. The speedometer suddenly jumps to around 5 km/h, the tunnel is brightly lit from below (and above) and you hear a whistle, sometimes a short scraping noise. The train starts to move and accelerates quickly and continuously, which can also be seen on the speed indicator. At the exit points we reach (if I remember correctly) around 60 km/h, which the driver comments on in disbelief: With the existing Locomotive Ge 4/4 III called “Tunnelmolch” we must be happy if we sneak out of here at 5 to 10 km/h.
Admittedly, the HGe 4/4 II has a lot more adhesive weight on the rails than the Ge 4/4 III and it also has a significantly higher torque (= tractive effort) in the low speed range due to the tractive effort required on the rack. The fact that this can also be utilized is thanks to the fast controlled skid protection.
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